$ 454,086

^[1]

$ 316,861

$ 198,141

^[2]

24,811

17,609

9,575

429,275

299,252

188,566

Product, technology, and development

315,939

236,165

154,125

47,866

22,470

11,453

General and administrative

39,475

22,688

12,783

Depreciation and amortization

2,804

2,655

1,634

406,084

283,978

179,995

23,191

^[1]

15,274

8,571

Interest income

2,283

869

416

Other income (expense)

(306)

(42)

Total other income, net

2,293

563

374

25,484

15,837

8,945

(39,686)

2,638

2,448

Reconciliation of net income to net income (loss) attributable to common stockholders:

65,170

13,199

6,497

Deemed dividend to preferred stockholders

65,170

13,199

6,497

(32,087)

Net income attributable to participating securities

(6,098)

Net income (loss) attributable to common stockholders — basic

65,170

7,101

(25,590)

Deemed dividend to preferred stockholders

65,170

13,199

6,497

(32,087)

Net income attributable to participating securities

(5,829)

Net income (loss) attributable to common stockholders — diluted

$ 65,170

$ 7,370

$ (25,590)

Net income (loss) per share attributable to common stockholders: (Note 9)

$ 0.60

$ 0.13

$ (0.58)

Weighted–average number of shares of common stock used in computing net income (loss) per share attributable to common stockholders:

$ 0.57

$ 0.12

$ (0.58)

108,833,028

55,835,265

44,138,922

113,364,712

60,637,584

44,138,922

[1]	Included in the year ended December 31, 2018 United States and International segments are revenue adjustments of $94 and $32, respectively, and operating income adjustments of $8,613 and $811, respectively, related to the Company's adoption of ASC 606.
[2]	Includes depreciation and amortization expense for the years ended December 31, 2018, 2017, and 2016 of $2,225 $1,140, and $438, respectively.

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 65,170	$ 13,199	$ 6,497
Other comprehensive income:
Foreign currency translation adjustment	(157)	258	(30)
Comprehensive income	$ 65,013	$ 13,457	$ 6,467

Organization and Business Description

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Series A Preferred Stock	Series B Preferred Stock	Series C Preferred Stock	Series D Preferred Stock	Series E Preferred Stock	Class A Common Stock	Class B Common Stock	Common Stock Class A Common Stock	Common Stock Class B Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Retained Earnings (Accumulated Deficit)
Beginning balance at Dec. 31, 2015	$ (16,131)								$ 15	$ 30	$ 2,434		$ (18,610)
Convertible preferred stock, Beginning balance, Shares at Dec. 31, 2015		3,049,606	3,296,054	1,567,855	1,673,105
Convertible preferred stock, Beginning balance at Dec. 31, 2015		$ 1,601	$ 2,574	$ 1,331	$ 67,872
Beginning balance, Shares at Dec. 31, 2015									14,879,954	29,759,908
Net income	6,497												6,497
Stock–based compensation expense	322										322
Issuance of common stock upon exercise of stock options	137										137
Issuance of common stock upon exercise of stock options, Shares									41,224	82,448
Tax benefit related to exercise of stock options	821										821
Convertible preferred stock, Issuance of preferred stock, net of issuance costs, Shares						1,107,202
Convertible preferred stock, Issuance of preferred stock, net of issuance costs						$ 59,732
Repurchase of stock	(59,588)	$ (118)	$ (279)	$ (15)					$ (1)	$ (2)			(59,585)
Repurchase of stock, Shares		(224,903)	(357,568)	(17,243)					(899,046)	(1,798,092)
Foreign currency translation adjustment	(30)											$ (30)
Ending balance at Dec. 31, 2016	(67,972)								$ 14	$ 28	3,714	(30)	(71,698)
Convertible preferred stock, Ending balance, Shares at Dec. 31, 2016		2,824,703	2,938,486	1,550,612	1,673,105	1,107,202
Convertible preferred stock, Ending balance at Dec. 31, 2016		$ 1,483	$ 2,295	$ 1,316	$ 67,872	$ 59,732
Ending balance, Shares at Dec. 31, 2016									14,022,132	28,044,264
Net income	13,199												13,199
Stock–based compensation expense	5,204										5,204
Issuance of common stock upon exercise of stock options	398										398
Issuance of common stock upon exercise of stock options, Shares									92,944	181,840
Issuance of stock, net of issuance/offering costs	43,240								$ 3		43,237
Issuance of stock, net of issuance/offering costs, Shares									3,205,000
Conversion of preferred and common stock	132,698								$ 61		132,637
Convertible preferred stock, Conversion of preferred stock, Shares		(2,824,703)	(2,938,486)	(1,550,612)	(1,673,105)	(1,107,202)
Convertible preferred stock, Conversion of preferred stock		$ (1,483)	$ (2,295)	$ (1,316)	$ (67,872)	$ (59,732)
Conversion of preferred and common stock, shares issued									60,564,678
Foreign currency translation adjustment	258											258
Ending balance at Dec. 31, 2017	127,025								$ 78	$ 28	185,190	228	(58,499)
Ending balance, Shares at Dec. 31, 2017							77,884,754	28,226,104	77,884,754	28,226,104
Net income	65,170												65,170
Stock–based compensation expense	21,284										21,284
Issuance of common stock upon exercise of stock options	3,632								$ 3		3,629
Issuance of common stock upon exercise of stock options, Shares									3,186,489	10,690
Issuance of common stock upon vesting of restricted stock units									$ 2		(2)
Issuance of common stock upon vesting of restricted stock units, Shares									1,781,201
Payment of withholding taxes on net share settlements of equity awards	(25,885)										(25,885)
Payment of withholding taxes on net share settlements of equity awards, Shares									(658,931)
Cumulative adjustment from adoption of revenue recognition standard (Note 2)	3,042												3,042
Conversion of preferred and common stock									$ 7
Conversion of preferred and common stock, shares issued									7,534,710
Conversion of preferred and common stock, shares converted										(7,534,710)
Conversion of preferred and common stock, value										$ (7)
Foreign currency translation adjustment	(157)											(157)
Ending balance at Dec. 31, 2018	$ 194,111								$ 90	$ 21	$ 184,216	$ 71	$ 9,713
Ending balance, Shares at Dec. 31, 2018							89,728,223	20,702,084	89,728,223	20,702,084

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Activities
Net income	$ 65,170	$ 13,199	$ 6,497
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	5,029	3,795	2,072
Unrealized currency (gain) loss on foreign denominated transactions	(190)	128
Deferred taxes	(39,040)	(1,117)	782
Provision for doubtful accounts	1,680	1,117	508
Stock–based compensation expense	20,794	5,028	322
Amortization of deferred contract costs	3,689
Excess tax benefit related to exercise of stock options			(821)
Changes in operating assets and liabilities:
Accounts receivable, net	(1,911)	(7,039)	(1,432)
Prepaid expenses, prepaid income taxes, and other assets	(11,753)	(2,287)	(2,226)
Deferred contracts costs	(12,987)
Accounts payable	9,345	6,244	5,811
Accrued expenses, accrued income taxes and other current liabilities	2,695	5,191	4,118
Deferred revenue	4,508	962	1,856
Deferred rent	4,289	227	1,927
Other non–current liabilities	405	243	590
Net cash provided by operating activities	51,723	25,691	20,004
Investing Activities
Purchases of property and equipment	(5,956)	(5,157)	(5,846)
Capitalization of website development costs	(1,522)	(2,215)	(1,372)
Investments in certificates of deposit	(212,800)	(50,000)	(59,774)
Maturities of certificates of deposit	140,000	44,774	15,000
Net cash used in investing activities	(80,278)	(12,598)	(51,992)
Financing Activities
Initial public offering proceeds		47,690
Payment of initial public offering costs	(1,142)	(3,308)
Proceeds from issuance of preferred stock			59,732
Proceeds from exercise of stock options	3,632	398	137
Excess tax benefit related to exercise of stock options			821
Cash paid for repurchase of preferred stock, common stock, and vested options			(60,000)
Payment of withholding taxes on net share settlements of equity awards	(25,885)
Net cash (used in) provided by financing activities	(23,395)	44,780	690
Impact of foreign currency on cash, cash equivalents, and restricted cash	(44)	159	(45)
Net (decrease) increase in cash, cash equivalents, and restricted cash	(51,994)	58,032	(31,343)
Cash, cash equivalents, and restricted cash at beginning of period	89,552	31,520	62,863
Cash, cash equivalents, and restricted cash at end of period	37,558	89,552	31,520
Supplemental disclosure of cash flow information:
Cash paid for income taxes	2,308	4,393	2,045
Cash paid for interest	19	29	26
Supplemental disclosure of non–cash investing and financing activities:
Unpaid purchases of property and equipment	5,287	510	$ 476
Unpaid initial public offering costs		1,142
Capitalized stock-based compensation in website development costs	$ 490	$ 176

Organization and Business Description

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

1. Organization and Business Description

CarGurus, Inc. (the “Company”), is a global, online automotive marketplace connecting buyers and sellers of new and used cars. Using proprietary technology, search algorithms, and innovative data analytics, the Company provides information and analysis that create a differentiated automotive search experience for consumers. The Company’s marketplace empowers users worldwide with unbiased third-party validation on pricing and dealer reputation, as well as other useful information that aids them in finding “Great Deals from Top-Rated Dealers.”

The Company is headquartered in Cambridge, Massachusetts and was incorporated in the State of Delaware on June 26, 2015. Prior to June 26, 2015, the Company operated as CarGurus LLC and was organized on November 10, 2005 as a limited liability company under the laws of the Commonwealth of Massachusetts. The Company operates principally in the United States and has also launched marketplaces in Canada, the United Kingdom, Germany, Italy, and Spain. The Company has wholly owned subsidiaries in the United States, Canada, Ireland, and the United Kingdom.

On October 16, 2017, the Company completed its initial public offering (“IPO”), in which the Company issued and sold 3,205,000 shares of its Class A common stock, including the full exercise by the underwriters of their option to purchase 705,000 shares of Class A common stock, at a public offering price of $16.00 per share for aggregate gross proceeds of $51.3 million. The Company received $43.2 million in net proceeds after deducting $3.6 million of underwriting discounts and commissions and $4.5 million in offering costs. In addition to shares of Class A common stock issued and sold by the Company, certain selling stockholders sold an aggregate of 7,605,000 shares of Class A common stock, including the full exercise by the underwriters of their option to purchase 705,000 shares of Class A common stock, as part of the IPO. Upon the closing of the IPO, all of the outstanding shares of convertible preferred stock automatically converted into 20,188,226 shares of Class A common stock and 40,376,452 shares of Class B common stock. The 40,376,452 shares of Class B common stock subsequently converted into 40,376,452 shares of Class A common stock resulting in a total conversion of all outstanding shares of convertible preferred stock into 60,564,678 shares of Class A common stock. Subsequent to the closing of the IPO, there were no shares of convertible preferred stock outstanding.

The Company is subject to a number of risks and uncertainties common to companies in its and similar industries and stages of development including, but not limited to, rapid technological changes, competition from substitute products and services from larger companies, management of international activities, protection of proprietary rights, patent litigation, and dependence on key individuals.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

The accompanying consolidated financial statements reflect the application of certain significant accounting policies as described below and elsewhere in these notes to the consolidated financial statements. The Company believes that a significant accounting policy is one that is both important to the portrayal of the Company’s financial condition and results, and requires management’s most difficult, subjective, or complex judgments, often as the result of the need to make estimates about the effect of matters that are inherently uncertain.

Basis of Presentation

The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative U.S. generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).

In the consolidated statements of operations for the years end ended December 31, 2017 and 2016, the Company has separately presented interest income from other income, net to conform to current year presentation due to the increase in amount during the year ended December 31, 2018 as compared to the year ended December 31, 2017 and 2016.

In the consolidated balance sheet as of December 31, 2017, the Company has separately presented other current assets from prepaid expenses and prepaid income taxes to conform to current year presentation due to the increase in the balance at December 31, 2018 as compared to December 31, 2017.

Principles of Consolidation

The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosures of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period.

Significant estimates relied upon in preparing these consolidated financial statements include revenue recognition and revenue reserves, contingent liabilities, allowances for doubtful accounts, expected future cash flows used to evaluate the recoverability of long‑lived assets, the expensing and capitalization of product, technology, and development costs for website development and internal‑use software, the determination of the fair value of stock awards issued prior to the IPO, stock‑based compensation expense, and the recoverability of the Company’s net deferred tax assets.

Although the Company regularly assesses these estimates, actual results could differ materially from these estimates. Changes in estimates are recorded in the period in which they become known. The Company bases its estimates on historical experience and various other assumptions that it believes to be reasonable under the circumstances. Actual results may differ from management’s estimates if these results differ from historical experience, or other assumptions do not turn out to be substantially accurate, even if such assumptions are reasonable when made.

Subsequent Events Considerations

The Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the financial statements to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. Subsequent events have been evaluated as required. The Company has evaluated all subsequent events and determined that there are no material recognized or unrecognized subsequent events requiring disclosure, other than those disclosed in this Annual Report on Form 10-K.

Revenue Recognition

The Company derives its revenue from two primary sources: (1) marketplace subscription revenue, which consists of listing subscriptions, display advertising subscriptions with dealers and dealer search engine marketing subscriptions, and (2) advertising and other revenue, which consists primarily of display advertising revenue from auto manufacturers and other auto‑related brand advertisers.

Marketplace Subscription Revenue

The Company offers three types of marketplace Listing products to dealers: Basic Listing, which is free; and Enhanced or Featured Listing, which require a paid subscription under a monthly, quarterly, semiannual, or annual subscription basis. Contractual subscriptions for customers generally auto‑renew on a monthly basis and are cancellable by dealers with 30‑days’ advance notice. The Company also offers Listing dealers access to the Dealer Dashboard, which includes a performance summary, Dealer Insights tool, user review management platform, Pricing Tool, and Market Analysis tool. The Pricing Tool and Market Analysis tool are available only to paying dealers. Subscription pricing is determined based on a dealer’s inventory size, region, and the Company’s assessment of the connections and Return on Investment (“ROI”) the platform will provide them.

Customers do not have the right to take possession of the Company’s software.

In addition to listing inventory in the marketplace and providing access to the Dealer Dashboard, the Company offers Enhanced and Featured Listing dealers other subscription advertising and customer acquisition products, including display advertising that appears in the Company’s marketplace and on other sites on the internet. This advertising can be targeted by geography, search history, and a number of other factors, and dealer search engine marketing, which helps dealers more effectively acquire customers through paid search, social media, and retargeted advertising.

Payment is typically due on first day of each calendar month and is recorded as accounts receivable or short-term deferred revenue when payment is received in advance of services being delivered to the customers.

Advertising and Other Revenue

Advertising and other revenue consists primarily of non-dealer display advertising revenue from auto manufacturers and other auto-related brand advertisers sold on a cost per thousand impressions (“CPM”) basis. An impression is an advertisement loaded on a web page. In addition to advertising sold on a CPM basis, the Company also has advertising sold on a cost per click basis. Auto manufacturers and other brand advertisers can execute advertising campaigns that are targeted across a wide variety of parameters, including demographic groups, behavioral characteristics, specific auto brands, categories such as Certified Pre-Owned, and segments such as hybrid vehicles. The Company does not provide minimum impression guarantees or other types of minimum guarantees in its contracts with customers. Pricing is primarily based on advertisement size and position on the Company’s websites and mobile applications, and fees are billed monthly in arrears. Unbilled accounts receivables relate to services rendered in the current period, but not invoiced until the subsequent period.

The Company sells advertising directly to auto manufacturers and other auto related brand advertisers, as well as indirectly through revenue sharing arrangements with advertising exchange partners. Company-sold advertising is not subject to revenue sharing arrangements. Company-sold advertising revenue is recognized based on the gross amount charged to the advertiser. Partner-sold advertising revenue is recognized based on the net amount of revenue received from the content partners.

Revenue from advertising sold directly by the Company is recorded on a gross basis because the Company is the principal in the arrangement, controls the ad placement and timing of the campaign, and establishes the selling price. The Company enters into contractual arrangements directly with advertisers and is directly responsible for the fulfillment of the contractual terms including any remedy for issues with such fulfillment.

Advertising revenue subject to revenue sharing agreements between the Company and advertising exchange partners is recognized based on the net amount of revenue received from the partner. The advertising partner is responsible for fulfillment, including the acceptability of the services delivered. In partner-sold advertising arrangements, the advertising partner has a direct contractual relationship with the advertiser. There is no contractual relationship between the Company and the advertiser for partner sold transactions. When an advertising exchange partner sells advertisements, the partner is responsible for fulfilling the advertisements, and accordingly, the Company has determined the advertising partner is the principal in the arrangement. Additionally, for auction-based partner agreements, the Company has latitude in establishing the floor price, but the final price is established by the exchange server are market rates.

Customers are billed monthly in arrears and payment terms are generally thirty to sixty days from the date invoiced.

Prior to adoption of ASC 606

The Company recognizes revenue when all of the following conditions are satisfied: (1) there is persuasive evidence of an arrangement; (2) the service has been provided to the customer; (3) the collection of fees is reasonably assured; and (4) the amount of fees to be paid by the customer is fixed or determinable.

The Company recognizes marketplace subscription revenue on a monthly basis as revenue is earned and advertising and other revenue as impressions are delivered. Revenue is presented net of any taxes collected from customers.

The Company assesses arrangements with multiple deliverables under ASU No. 2009‑13, Revenue Recognition (Topic 605), Multiple‑Deliverable Revenue Arrangements — a Consensus of the FASB Emerging Issues Task Force. Pursuant to ASU 2009‑13, in order to treat deliverables in a multiple‑element arrangement as separate units of accounting, the deliverables must have stand‑alone value upon delivery. If the deliverables have stand‑alone value upon delivery, the Company accounts for each deliverable separately. The Company has concluded that each element in the arrangement has stand‑alone value as the individual services can be sold separately. In addition, there is no right of refund once a service has been delivered. Therefore, the Company has concluded each element of the arrangement is a separate unit of accounting. While these arrangements are considered multiple element‑arrangements, the recognition of the units of accounting follow a consistent ratable recognition given the pattern over which services are provided.

The Company establishes sales allowances at the time of revenue recognition based on its history of adjustments and credits provided to its customers. Sales allowances relate primarily to credits issued for service interruption. In assessing the adequacy of the sales allowance, the Company evaluates its history of adjustments and credits made through the date of the issuance of the financial statements. Estimated sales adjustments and credits and ultimate losses may vary from actual results which could be material to the financial statements; however, to date, actual sales allowances have been materially consistent with the Company’s estimates. Sales allowances are recorded as a reduction to revenue in the consolidated statements of operations.

Post adoption of ASC 606

In May 2014, the Financial Accounting Standards Board (FASB) issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which modifies how all entities recognize revenue, and consolidates revenue recognition guidance into one ASC Topic (ASC Topic 606, Revenue from Contracts with Customers) (“ASC 606”). Since the Company ceased to be an emerging growth company as of December 31, 2018, the Company adopted the standard during the fourth quarter of 2018 and applied the modified retrospective method of adoption with a cumulative catch-up adjustment to the opening balance of retained earnings at January 1, 2018. Under this method, the Company applied the revised guidance for the year of adoption and applied ASC Topic 605, Revenue Recognition (“ASC 605”), in the prior years. As a result, the Company applied ASC 606 only to contracts that were not yet completed as of January 1, 2018. The Company recognized a cumulative catch-up adjustment to the opening balance of retained earnings at the effective date for contracts that still required performance by the Company at January 1, 2018. For contracts that were modified before the effective date, the Company exercised the use of the practical expedient and reflected the aggregate effect of all modifications when identifying performance obligations, determining the transaction price and allocating transaction price, which did not have a material effect on the adjustment to retained earnings.

ASC 606 outlines a comprehensive five-step revenue recognition model based on the principle that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve this core principle, the Company applies the following five steps:

Identify the contract with a customer

Identify the performance obligations in the contract

Determine the transaction price

Allocate the transaction price to performance obligations in the contract

Recognize revenue when or as the Company satisfies a performance obligation

Disaggregation of Revenue

The following table summarizes revenue from contracts with customers by revenue source for the year ended December 31, 2018.

	Year Ended
	December 31, 2018
Revenue by Revenue Stream
Marketplace subscription revenue	$	405,780
Advertising and other revenue		48,306
Total	$	454,086

The Company provides disaggregation of revenue based on the marketplace subscription versus advertising and other revenue classification in the table above and based on geographic region (see Note 11) as it believes these categories best depict how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors.

Marketplace Subscription Revenue

For dealer listings, the Company provides a single similar service each day for a period of time. Each time increment (i.e. day), rather than the underlying activities, is distinct and substantially the same and therefore the performance obligation of the Company is to provide a series of daily activities over the contract term. Similar to the dealer listings, the display advertising is considered a promise to provide a single similar service each day. Each time increment is distinct and substantially the same and therefore the performance obligation of the Company is to provide a series of daily activities over the contract term.

Total consideration for marketplace subscription revenue is stated within the contracts. There are no contractual cash refund rights, but credits may be issued to a customer at the sole discretion of the Company. At an individual contract level, there is also no variable consideration, such as sales allowance, that needs to be included in the transaction price. However, at a portfolio level, the Company recognizes that there are times when there is a customer satisfaction issue or other circumstance that will lead to a credit. Due to the known possibility of future credits, a monthly sales allowance review is performed to defer revenue at a portfolio level for such future adjustments in the period of incurrence. The Company establishes sales allowances at the time of revenue recognition based on its history of adjustments and credits provided to its customers. In assessing the adequacy of the sales allowance, the Company evaluates its history of adjustments and credits made through the date of the issuance of the financial statements. Estimated sales adjustments, credits and losses may vary from actual results which could lead to material adjustments to the financial statements. To date, actual sales allowances have been materially consistent with the Company’s estimates. Sales allowances are recorded as a reduction to revenue in the consolidated statements of operations.

Performance obligations are satisfied over time as the customer simultaneously receives and consumes the benefit of the service. Revenue is recognized ratably over the subscription period beginning on the date the Company’s online products are made available to the customers. Revenue is presented net of any taxes collected from customers.

Advertising and Other Revenue

For advertising revenue, the performance obligation is to publish the agreed upon campaign on the Company’s websites and load the related impressions.

Advertising contracts state the transaction price within the agreement with payment being based on the number of clicks or impressions delivered on the Company’s websites. Total consideration is based on output and deemed variable consideration constrained by an agreed upon delivery schedule. Additionally, there are generally no contractual cash refund rights. Certain contracts do contain the right for credits in situations in which impressions are not displayed in compliance with contractual specifications. At an individual contract level, the Company may give a credit for a customer satisfaction issue or other circumstance. Due to the known possibility of future credits, a monthly review is performed to defer revenue at an individual contract level for such future adjustments in the period of incurrence.

As consideration is driven by the number of impressions delivered on the CarGurus websites, the consideration for each period is allocated to the period in which the service was rendered.

Performance obligations for company-sold advertising revenue and partner-sold advertising revenue are satisfied over time as impressions are delivered. Revenue is recognized based on the total number of impressions delivered within the specified period. Revenue from advertising sold directly by the Company is recognized based on the gross amount charged to the advertiser and advertising revenue sold by partners is recognized based on the net amount of revenue received from the content partners. Revenue is presented net of any taxes collected from customers.

For other revenue, performance obligations are satisfied over time as services are rendered and revenue is recognized as it is earned.

Contracts with Multiple Performance Obligations

The Company periodically enters into arrangements that include Dealer Listing and Display within marketplace subscription revenue. These contracts include multiple promises that the Company evaluates to determine if the promises are separate performance obligations. Performance obligations are identified based on services to be transferred to a customer that are distinct within the context of the contractual terms. Once the performance obligations have been identified, the Company determines the transaction price, which includes estimating the amount of variable consideration to be included in the transaction price, if any. If required, the transaction price is allocated to each performance obligation in the contract based on a relative SSP method as the performance obligation is being satisfied. For the Company’s arrangements that include Dealer Listing and Display, the performance obligations were satisfied over a consistent period of time and therefore the allocations did not impact the revenue recognized.

Costs to Obtain a Contract

Commissions paid to sales representatives and payroll taxes are considered costs to obtain a contract. Under the new guidance, the costs to obtain a contract require capitalization and amortization of those costs over the period of benefit. Although the new guidance specifies the accounting for an individual contract with a customer, as a practical expedient, the Company has opted to apply the guidance to a portfolio of contracts with similar characteristics. The Company has opted to apply another practical expedient to immediately expense the incremental cost of obtaining a contract when the underlying related asset would have been amortized over one year or less. As such, the Company applied this practical expedient to advertising contracts as the term is one year or less and these contracts do not renew automatically. The practical expedient is not applicable to marketplace subscription contracts as the period of benefit including renewals is anticipated to be greater than one year as commissions paid on contract renewals are not commensurate with the commissions paid on the initial contract. The assets are periodically assessed for impairment.

For marketplace subscription customers, the commissions paid on contracts with new customers, in addition to any commission amount related to incremental sales, are capitalized and amortized over the estimated benefit period of the customer relationship taking into account factors such as peer estimates of technology lives and customer lives as well as the Company's own historical data. Commissions paid that are not directly related to obtaining a new contract are expensed as incurred.

Additionally, the Company allocates employer payroll tax expense to the commission expense in proportion to the overall payroll taxes paid during the respective period. As such, capitalized payroll taxes are amortized in the same manner as the underlying capitalized commissions.

Financial Statement Impact of Adopting ASC 606

The cumulative effect of applying the new guidance to all contracts with customers that were not completed as of January 1, 2018 was recorded as an adjustment to accumulated deficit as of the adoption date. As a result of applying the modified retrospective method to adopt the new revenue guidance, the following adjustments were made on the consolidated balance sheet as of January 1, 2018.

	As Reported			Adjustments						As Adjusted
	December 31, 2017			Marketplace Subscription Revenue			Costs to Obtain a Contract			January 1, 2018
Assets
Current assets:
Cash and cash equivalents	$	87,709								$	87,709
Investments		50,000									50,000
Accounts receivable, net		12,577			813						13,390
Prepaid expenses and prepaid income taxes		5,313									5,313
Deferred contract costs		—						1,424			1,424
Other current assets		1,605									1,605
Restricted cash		—									—
Total current assets		157,204			813			1,424			159,441
Property and equipment, net		16,563									16,563
Restricted cash		1,843									1,843
Deferred tax assets		825			(190	)		(635	)		—
Deferred contract costs, net of current portion		—						1,783			1,783
Other long–term assets		159									159
Total assets	$	176,594		$	623		$	2,572		$	179,789
Liabilities and stockholders’ equity
Current liabilities:
Accounts payable	$	23,908								$	23,908
Accrued expenses, accrued income taxes and other current liabilities		13,588									13,588
Deferred revenue		4,305									4,305
Deferred tax liabilities		—						153			153
Deferred rent		1,165									1,165
Total current liabilities		42,966			—			153			43,119
Deferred rent, net of current portion		5,648									5,648
Other non–current liabilities		955									955
Total liabilities		49,569			—			153			49,722
Commitments and contingencies
Stockholders’ equity:
Preferred stock		—									—
Class A common stock		78									78
Class B common stock		28									28
Additional paid–in capital		185,190									185,190
Accumulated deficit		(58,499	)		623			2,419			(55,457	)
Accumulated other comprehensive income		228									228
Total stockholders’ equity		127,025			623			2,419			130,067
Total liabilities and stockholders’ equity	$	176,594		$	623		$	2,572		$	179,789

Marketplace Subscription Revenue

Under ASC 606, the Company’s accounting for contracts containing discounts resulted in accelerated revenue recognition. The cumulative impact of this change to the Company’s accounts receivable on January 1, 2018 was $813.

Costs to Obtain a Contract

As described above, under the new guidance, the capitalized commission expense is amortized over the estimated customer relationship period. The net impact of this change resulted in a $3,207 reduction to accumulated deficit for contracts that still require performance by the Company at the date of adoption.

Income Taxes

The adoption of ASC 606 primarily resulted in an acceleration of revenue and the reduction of expense, which in turn generated additional deferred tax liabilities that ultimately reduced the Company’s net deferred tax asset position. The cumulative impact resulted in a reduction to deferred tax assets of $978 which put the Company in a net deferred tax liability position on January 1, 2018.

Impact of New Revenue Guidance on Financial Statement Line Items

The following tables compare the reported consolidated balance sheet, statement of operations and cash flows, as of and for the year ended December 31, 2018, to the pro-forma amounts had the previous guidance been in effect.

	As of December 31, 2018
Balance Sheet	As Reported		Marketplace Subscription Revenue			Costs to Obtain a Contract			Pro forma as if the previous accounting guidance was in effect
Assets
Current assets:
Cash and cash equivalents	$	34,887							$	34,887
Investments		122,800								122,800
Accounts receivable, net		13,614		939						12,675
Prepaid income taxes and prepaid income taxes		10,144								10,144
Deferred contract costs		5,253					5,253			—
Other current assets		7,410								7,410
Restricted cash		750								750
Total current assets		194,858		939			5,253			188,666
Property and equipment, net		24,269								24,269
Restricted cash		1,921								1,921
Deferred tax assets		38,886		(227	)		(3,187	)		42,300
Deferred contract costs, net of current portion		7,252					7,252			—
Other long–term assets		1,104								1,104
Total assets	$	268,290	$	712		$	9,318		$	258,260
Liabilities and stockholders’ equity
Current liabilities:
Accounts payable	$	34,345							$	34,345
Accrued expenses, accrued income taxes and other current liabilities		18,654								18,654
Deferred revenue		8,811								8,811
Deferred rent		1,693								1,693
Total current liabilities		63,503		—			—			63,503
Deferred rent, net of current portion		9,395								9,395
Other non–current liabilities		1,281								1,281
Total liabilities		74,179		—			—			74,179
Commitments and contingencies
Stockholders’ equity:
Preferred stock		—								—
Class A common stock		90								90
Class B common stock		21								21
Additional paid–in capital		184,216								184,216
Retained earnings (accumulated deficit)		9,713		712			9,318			(317	)
Accumulated other comprehensive income		71								71
Total stockholders’ equity		194,111		712			9,318			184,081
Total liabilities and stockholders’ equity	$	268,290	$	712		$	9,318		$	258,260

Total reported assets were $10,030 greater than the pro-forma balance sheet, which assumes the previous guidance remained in effect as of December 31, 2018. This was largely due to the impact of $12,505 related to costs to obtain a contract.

There were no changes to liabilities as of December 31, 2018 as a result of the adoption of ASC 606.

The following summarizes the significant changes on the Company’s consolidated statement of operations for the year ended December 31, 2018 as a result of the adoption of ASC 606 on January 1, 2018 compared to the pro-forma amounts had the Company continued to recognize revenue under ASC 605.

	Year Ended December 31, 2018
Statement of Operations	As Reported			Marketplace Subscription Revenue		Costs to Obtain a Contract			Pro forma as if the previous accounting guidance was in effect
Revenue	$	454,086		$	126				$	453,960
Cost of revenue		24,811								24,811
Gross profit		429,275			126		—			429,149
Operating expenses:
Sales and marketing		315,939					(9,298	)		325,237
Product, technology, and development		47,866								47,866
General and administrative		39,475								39,475
Depreciation and amortization		2,804								2,804
Total operating expenses		406,084			—		(9,298	)		415,382
Income from operations		23,191			126		9,298			13,767
Other income, net:
Interest income		2,283								2,283
Other income (expense)		10								10
Total other income, net		2,293			—		—			2,293
Income before income taxes		25,484			126		9,298			16,060
(Benefit from) provision for income taxes		(39,686	)		37		2,399			(42,122	)
Net income	$	65,170		$	89	$	6,899		$	58,182
Basic	$	0.60		$	—	$	0.07		$	0.53
Diluted	$	0.57		$	—	$	0.06		$	0.51

The adoption of ASC 606 resulted in an increase to revenue of $126 during the year ended December 31, 2018 due to accelerated revenue recognition for contracts containing discounts. The adoption of ASC 606 also resulted in a $9,298 reduction in sales and marketing expense during the year ended December 31, 2018 as a result of capitalizing a portion of commission expense, which was previously expensed under the previous guidance. During the year ended December 31, 2018, the cumulative impact of these changes was a $9,424 increase in income from operations which resulted in a $2,436 reduction to the benefit from income taxes. Additionally, the adoption of ASC 606 resulted in the Company’s basic and diluted EPS for the year ended December 31, 2018 increasing $0.07 and $0.06, respectively.

The following summarizes the significant changes on the Company’s consolidated statement of cash flows for the year ended December 31, 2018 as a result of the adoption of ASC 606 on January 1, 2018 compared to the pro-forma amounts had the Company continued to recognize revenue under ASC 605.

	Year Ended December 31, 2018
Statement of Cash Flows	As Reported			Marketplace Subscription Revenue			Costs to Obtain a Contract			Pro forma as if the previous accounting guidance was in effect
Operating Activities
Net income	$	65,170		$	89		$	6,899		$	58,182
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		5,029									5,029
Unrealized currency (gain) loss on foreign denominated transactions		(190	)								(190	)
Deferred taxes		(39,040	)		37			2,399			(41,476	)
Provision for doubtful accounts		1,680									1,680
Stock–based compensation expense		20,794									20,794
Amortization of deferred contract costs		3,689						3,689			—
Changes in operating assets and liabilities:
Accounts receivable, net		(1,911	)		(126	)					(1,785	)
Prepaid expenses, prepaid income taxes, and other assets		(11,753	)								(11,753	)
Deferred contracts costs		(12,987	)					(12,987	)		—
Accounts payable		9,345									9,345
Accrued expenses, accrued income taxes and other current liabilities		2,695									2,695
Deferred revenue		4,508									4,508
Deferred rent		4,289									4,289
Other non–current liabilities		405									405
Net cash provided by operating activities		51,723			—			—			51,723

The adoption of ASC 606 had no impact on the Company’s cash flows from operations. The aforementioned impacts resulted in offsetting shifts in cash flows between net income and various working capital balances.

The following summarizes the opening and closing balances of receivables and contract assets from contracts with customers.

Accounts

Receivable, net

Contract Assets

(current)

Contract Assets

(non-current)

Balance at January 1, 2018

13,390

1,424

1,783

Balance at December 31, 2018

13,614

5,253

7,252

The assets recognized for costs to obtain a contract was $3,207 and $12,505 as of January 1, 2018 and December 31, 2018, respectively. Amortization expense recognized during the year ended December 31, 2018 related to costs to obtain a contract were $3,689.

Transaction Price Allocated to Future Performance Obligations

ASC 606 requires that the Company disclose the aggregate amount of transaction price that is allocated to performance obligations that have not yet been satisfied as of December 31, 2018. However, the Company applied the practical expedient to not disclose the amount of transaction price allocated to unsatisfied performance obligations when the performance obligation is part of a contract that has an original expected duration of one year or less.

The Company does not have future obligations associated with marketplace revenue subscriptions or advertising and other services that extend beyond one year. For performance obligations not satisfied as of December 31, 2018, the nature of the performance obligations, the variable consideration and any consideration from contracts with customers not included in the transaction price is consistent with performance obligations satisfied as of December 31, 2018. The remaining duration is less than one year.

Deferred Revenue

Deferred revenue primarily consists of payments received in advance of revenue recognition from the Company’s marketplace revenue and is recognized as the revenue recognition criteria are met. The Company generally invoices its customers monthly. Accordingly, the deferred revenue balances do not represent the total contract value of annual or multiyear subscription agreements. Deferred revenue that is expected to be recognized during the succeeding 12‑month period is recorded as current deferred revenue and the remaining portion is recorded as noncurrent in the consolidated balance sheets. All deferred revenue was recorded as current for all periods presented.

Cost of Revenue

Cost of revenue primarily consists of costs related to supporting and hosting the Company’s websites and product offerings. These costs include salaries, benefits, incentive compensation and stock‑based compensation expense related to the customer support team, and third‑party service provider costs such as data center and networking expenses, allocated overhead, depreciation and amortization expense associated with the Company’s property and equipment, and amortization of capitalized website development costs.

Concentration of Credit Risk

The Company has no significant off‑balance sheet risk, such as foreign exchange contracts, option contracts, or other foreign hedging arrangements. Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents, investments, and trade accounts receivable. The Company maintains its cash, cash equivalents, and investments principally with accredited financial institutions of high credit standing. Although the Company deposits its cash and investments with multiple financial institutions, its deposits, at times, may exceed federally insured limits.

Credit risk with respect to accounts receivable is dispersed due to the large number of customers. The Company routinely assesses the creditworthiness of its customers. The Company generally has not experienced any material losses related to receivables from individual customers, or groups of customers. The Company does not require collateral. Due to these factors, no additional credit risk beyond amounts provided for collection losses is believed by management to be probable in the Company’s accounts receivable.

For the years ended December 31, 2018, 2017 and 2016, no individual customer accounted for more than 10% of total revenue.

As of December 31, 2018, two customers accounted for 21% and 14% of net accounts receivable, respectively. As of December 31, 2017, two customers accounted for 29% and 17% of net accounts receivable, respectively. No other individual customer accounted for more than 10% of net accounts receivable at December 31, 2018 or 2017.

Included in net accounts receivable at December 31, 2018 and 2017, is $5,815 and $1,845 of unbilled accounts receivables related to advertising customers billed within a quarter subsequent to services rendered.

Cash, Cash Equivalents, and Investments

The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. Investments not classified as cash equivalents with maturities less than one year from the balance sheet date are classified as short‑term investments, while investments with maturities in excess of one year from the balance sheet date are classified as long‑term investments. Management determines the appropriate classification of investments at the time of purchase, and re‑evaluates such determination at each balance sheet date.

Cash and cash equivalents primarily consist of cash on deposit with banks, and amounts held in interest‑bearing money market accounts. Cash equivalents are carried at cost, which approximates their fair market value.

The Company’s investment policy, which was approved by the Audit Committee of the Company’s board of directors (the “Board”), permits investments in fixed income securities, including U.S. government and agency securities, non‑U.S. government securities, money market instruments, commercial paper, certificates of deposit, corporate bonds, and asset‑backed securities.

As of December 31, 2018 and 2017, investments consisted of U.S. certificates of deposit (“CDs”) with remaining maturities of less than twelve months. The Company classifies CDs with readily determinable market values as held‑to‑maturity, because it is the Company’s intention to hold such investments until they mature. As such, investments were recorded at amortized cost at December 31, 2018 and 2017. The Company adjusts the cost of investments for amortization of premiums and accretion of discounts to maturity, if any. For the years ended December 31, 2018, 2017 and 2016, the Company did not have any premiums or discounts.

Realized gains and losses from sales of the Company’s investments are included in other income (expense). There were no realized gains or losses on investments for the years ended December 31, 2018, 2017 or 2016.

The Company reviews investments for other‑than‑temporary impairment whenever the fair value of an investment is less than the amortized cost and evidence indicates that an investment’s carrying amount is not recoverable within a reasonable period of time. Other‑than‑temporary impairments of investments are recognized in the consolidated statements of operations if the Company has experienced a credit loss, has the intent to sell the investment, or if it is more likely than not that the Company will be required to sell the investment before recovery of the amortized cost basis. Evidence considered in this assessment includes reasons for the impairment, compliance with the Company’s investment policy, the severity and duration of the impairment, and changes in value subsequent to the end of the period. As of December 31, 2018 and 2017, the Company determined that no other‑than‑temporary impairments were required to be recognized in the consolidated statements of operations.

Restricted Cash

At December 31, 2018 and 2017, restricted cash was $2,671 and $1,843, respectively, and primarily related to cash held at a financial institution in an interest‑bearing cash account as collateral for three letters of credit in 2018 and two letters of credit in 2017 related to the contractual provisions for the Company’s building lease security deposits.

Accounts Receivable and Allowance for Doubtful Accounts

Accounts receivable are recorded based on the amount due from the customer and do not generally bear interest. The Company offsets gross trade accounts receivable with an allowance for doubtful accounts. The allowance for doubtful accounts is the Company’s best estimate of the amount of probable credit losses in the Company’s existing accounts receivable and is based upon historical loss patterns, the number of days that billings are past due, and an evaluation of the potential risk of loss associated with specific accounts. Account balances are charged against the allowance after all means of collection have been exhausted and the potential for recovery is considered remote. The Company does not have any off‑balance sheet credit exposure related to its customers. Provisions for allowances for doubtful accounts are recorded in general and administrative expense.

Unbilled accounts receivables are recorded for services rendered in the current period, but not invoiced until the subsequent period.

The Company considers current economic trends when evaluating the adequacy of the allowance for doubtful accounts. If circumstances relating to specific customers change, or unanticipated changes occur in the general business environment, particularly as it affects auto dealers, the Company’s estimates of the recoverability of receivables could be further adjusted.

Below is a summary of the changes in the Company’s allowance for doubtful accounts for the years ended December 31, 2018, 2017, and 2016:

	Balance at Beginning of Period		Provision		Write–offs, net of recoveries			Balance at End of Period
Year ended December 31, 2018	$	494	$	1,680	$	(1,695	)	$	479
Year ended December 31, 2017		164		1,117		(787	)		494
Year ended December 31, 2016		75		508		(419	)		164

Property and Equipment

Property and equipment are stated at cost less accumulated depreciation and amortization using the straight‑line method over the estimated useful lives of the assets. Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the related asset. The estimated useful lives of the Company’s property and equipment are as follows:

	Estimated Useful Life (In Years)
Computer equipment	3
Capitalized software	3
Website development costs	3
Furniture and fixtures	5
Leasehold improvements	Lesser of asset life or lease term

Expenditures for maintenance and repairs are charged to expense as incurred, whereas major betterments are capitalized as additions to property and equipment. The Company reviews its property and equipment whenever events or changes in circumstances indicate that the carrying value of certain assets might not be recoverable. In these instances, the Company recognizes an impairment loss when it is probable that the estimated cash flows are less than the carrying value of the asset.

Foreign Currency Translation

The reporting currency of the Company is the U.S. dollar. The functional currency of the Company’s foreign subsidiaries is the local currency of each subsidiary. All assets and liabilities in the balance sheets of entities whose functional currency is a currency other than the U.S. dollar are translated into U.S. dollar equivalents at exchange rates as follows: (1) asset and liability accounts at period‑end rates; (2) income statement accounts at weighted‑average exchange rates for the period; and (3) stockholders’ equity accounts at historical exchange rates. The resulting translation adjustments are excluded from net income and reflected as a separate component of stockholders’ equity (deficit). Foreign currency transaction gains and losses are included in net income for the period. The Company may periodically have certain intercompany foreign currency transactions that are deemed to be of a long‑term investment nature; exchange adjustments related to those transactions are made directly to a separate component of stockholders’ equity (deficit).

Capitalized Website and Software Development Costs

The Company capitalizes certain costs associated with the development of its websites and internal‑use software products after the preliminary project stage is complete, and until the software is ready for its intended use. Research and development costs incurred during the preliminary project stage or costs incurred for data conversion activities, training, maintenance, and general and administrative or overhead costs are expensed as incurred. Capitalization begins when the preliminary project stage is complete; management authorizes and commits to the funding of the software project with appropriate authority; it is probable the project will be completed; the software will be used to perform the functions intended; and certain functional and quality standards have been met. Qualified costs incurred during the operating stage of the Company’s software applications relating to upgrades and enhancements are capitalized to the extent it is probable that they will result in added functionality, while costs that cannot be separated between maintenance of, and minor upgrades and enhancements to, internal‑use software are expensed as incurred.

Capitalized website development costs and software development costs are amortized on a straight‑line basis over their estimated useful life of three years beginning with the time when it is ready for intended use. Management evaluates the useful lives of these assets on an annual basis and tests for impairment whenever events or changes in circumstances occur that could impact the recoverability of these assets.

During the years ended December 31, 2018 and 2017, the Company capitalized $2,012 and $2,215 of website and software development costs, respectively. The Company recorded amortization expense associated with its capitalized website and software development costs of $1,508, $812, and $343 for the years ended December 31, 2018, 2017, and 2016, respectively.

Impairment of Long‑Lived Assets

The Company evaluates the recoverability of long‑lived assets, such as property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. During this review, the Company re‑evaluates the significant assumptions used in determining the original cost and estimated lives of long‑lived assets. Although the assumptions may vary from asset to asset, they generally include operating results, changes in the use of the asset, cash flows, and other indicators of value. Management then determines whether the remaining useful life continues to be appropriate, or whether there has been an impairment of long‑lived assets based primarily upon whether expected future undiscounted cash flows are sufficient to support the assets’ recovery. Recoverability of these assets is measured by comparison of the carrying amount of the asset to the future undiscounted cash flows the asset is expected to generate. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired asset.

For the years ended December 31, 2018, 2017, and 2016, the Company did not identify any impairment of its long‑lived assets.

Income Taxes

The Company accounts for income taxes in accordance with the asset and liability method. Under this method, deferred tax assets and liabilities are recognized based on temporary differences between the financial reporting and income tax bases of assets and liabilities using statutory rates. In addition, this method requires a valuation allowance against net deferred tax assets if, based upon the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

The Company accounts for uncertain tax positions recognized in the consolidated financial statements by prescribing a more‑likely‑than‑not threshold for financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. The Company has no recorded liabilities for uncertain tax positions as of December 31, 2018 and 2017.

Disclosure of Fair Value of Financial Instruments

The carrying amounts of the Company’s financial instruments, which include cash and cash equivalents, investments, accounts receivable, accounts payable, and accrued expenses, approximated their fair values at December 31, 2018 and 2017 due to the short‑term nature of these instruments.

The Company has evaluated the estimated fair value of financial instruments using available market information. The use of different market assumptions, estimation methodologies, or both, could have a significant effect on the estimated fair value amounts. See Note 3 for further discussion.

Stock‑Based Compensation

For stock‑based awards issued under the Company’s stock‑based compensation plans, which are more fully described in Note 8, the fair value of each award is estimated on the date of grant, and, up through the year ended December 31, 2016, an estimated forfeiture rate was used when calculating stock‑based compensation expense for the period. The Company recognizes compensation expense for service-based awards on a straight-line basis over the requisite service period for each separate vesting portion of the award, with the amount of compensation expense recognized at any date at least equaling the portion of the grant-date fair value of the award that is vested at that date.

Certain awards granted by the Company prior to the IPO were subject to service‑based vesting conditions and a performance‑based vesting condition achieved upon a liquidity event, defined as either a change of control or an initial public offering. The Securities and Exchange Commission’s declaration of effectiveness of the Company’s registration statement on Form S-1 on October 11, 2017 satisfied the liquidity event performance condition. Upon the achievement of the liquidity event, the Company recorded previously unrecognized cumulative stock-based compensation expense of $2.5 million related to these awards. Although the performance based vesting condition was satisfied, under the terms of the awards, the settlement of such vested RSUs and the issuance of common stock with respect to such vested RSUs, occurred on April 10, 2018, one hundred eighty-one days after the satisfaction of the performance condition.

Given the absence of an active market for the Company’s common stock prior to the IPO, the Board, the members of which the Company believes have extensive business, finance, and venture capital experience, was required to estimate the fair value of the Company’s common stock at the time of each grant of a stock‑based award. The Company and the Board utilized various valuation methodologies in accordance with the framework of the American Institute of Certified Public Accountants’ Technical Practice Aid, Valuation of Privately‑Held Company Equity Securities Issued as Compensation, to estimate the fair value of its common stock. Each valuation methodology includes estimates and assumptions that require the Company’s judgment. These estimates and assumptions include a number of objective and subjective factors in determining the value of the Company’s common stock at each grant date, including the following factors: (1) prices paid for the Company’s convertible Preferred Stock, which the Company had sold to outside investors in arm’s‑length transactions, and the rights, preferences, and privileges of the Company’s convertible Preferred Stock and common stock; (2) valuations performed by an independent valuation specialist; (3) the Company’s stage of development and revenue growth; (4) the fact that the grants of stock‑based awards involved illiquid securities in a private company; and (5) the likelihood of achieving a liquidity event for the common stock underlying the stock‑based awards, such as an IPO or sale of the Company, given prevailing market conditions.

The Company believes this methodology was reasonable based upon the Company’s internal peer company analyses, and further supported by arm’s‑length transactions involving the Company’s convertible Preferred Stock. As the Company’s common stock was not actively traded, the determination of fair value involved assumptions, judgments, and estimates. If different assumptions had been made, stock‑based compensation expense, consolidated net income, and consolidated net income (loss) per share could have been significantly different.

For RSUs granted subsequent to the IPO, the fair value is determined based on the closing price of the Company’s Class A common stock as reported on the Nasdaq Global Select Market on the date of grant.

For RSUs issued under the Company’s stock‑based compensation plans prior to the IPO, the fair value of each grant was calculated based on the estimated fair value of the Company’s common stock on the date of grant. The Company estimated the fair value of most stock option awards on the date of grant using the Black‑Scholes option‑pricing model. Certain stock option awards that have an exercise price that was materially above the current estimated fair market value of the Company’s stock are considered to be “deeply out of the money,” and are valued at the date of grant using a binomial lattice option‑pricing model.

The fair value of each option grant issued under the Company’s stock‑based compensation plans that was not considered “deeply out of the money,” was estimated using the Black‑Scholes option‑pricing model. As there was no public market for its common stock prior to the IPO, the Company determined the volatility for options granted based on an analysis of reported data for a peer group of companies that issued options with substantially similar terms. The expected volatility of granted options has been determined using a weighted‑average of the historical volatility measures of this peer group of companies. The expected life of options has been determined utilizing the “simplified method.” The simplified method is based on the average of the vesting tranches and the contractual life of each grant. The risk‑free interest rate is based on a treasury instrument whose term is consistent with the expected life of the stock options. The Company has not paid, and does not anticipate paying, cash dividends on its common stock; therefore, the expected dividend yield was assumed to be zero. In addition, the Company applied an estimated forfeiture rate of 5% in determining the expense recorded in the accompanying consolidated statements of operations for the year ended December 31, 2016.

The Company issues shares for stock option exercises and RSUs out of its shares available for issuance.

In March 2016, the FASB issued ASU 2016‑09, Compensation — Stock Compensation (Topic 718): Improvements to Employee Share‑Based Payment Accounting (ASU 2016‑09). The guidance identifies areas for simplification involving several aspects of accounting for share‑based payments, including income tax consequences, classification of awards as either equity or liabilities, an option to make a policy election to recognize gross stock‑based compensation expense with actual forfeitures recognized as they occur, as well as certain classification changes on the statement of cash flows. The Company adopted ASU 2016‑09 on January 1, 2017 and elected to account for forfeitures when they occur, on a modified retrospective basis. The cumulative effect adjustment related to the Company’s accounting policy change for forfeitures was not material. In accordance with the adoption of this guidance, the tax effect of differences between tax deductions related to stock compensation and the corresponding financial statement expense compensation will no longer be recorded to additional paid‑in capital in the balance sheet. Instead, such amounts will be recorded to tax expense. During 2018 and 2017, the Company recorded tax benefits of $40,765 and $681, respectively, related to differences between tax deductions related to stock compensation and the corresponding financial statement expense compensation. The Company also elected to prospectively apply the change in presentation of excess tax benefits, wherein excess tax benefits recognized on stock‑based compensation expense is now classified as an operating activity in the consolidated statements of cash flows. The Company did not adjust the classifications of excess tax benefits in its consolidated statements of cash flows for the years ended December 31, 2016. The adoption did not have any other material impact on the Company’s consolidated financial statements.

No options were granted during the years ended December 31, 2018 and 2017. The weighted‑average fair value of options granted during the year ended December 31, 2016 was $0.90. The weighted‑average assumptions utilized to determine the fair value of options granted are presented in the following table:

	2016
Expected dividend yield		—
Expected volatility		49	%
Risk–free interest rate		1.57	%
Expected term (in years)		6.07

See Note 8 for a summary of the stock option and RSU activity for the year ended December 31, 2018.

Advertising Costs

Advertising costs are expensed as incurred. Advertising expense, which is included within sales and marketing expense in the consolidated statements of operations, was $238,640, $173,186, and $112,167 for the years ended December 31, 2018, 2017, and 2016, respectively.

Leases

The Company categorizes leases at their inception as either operating or capital leases. On certain lease arrangements, the Company may receive rent holidays or other incentives. The Company recognizes lease costs on a straight‑line basis once control of the space is achieved, without regard to deferred payment terms, such as rent holidays, that defer the commencement date of required payments or escalating payment amounts. The difference between required lease payments and rent expense has been recorded as deferred rent. Additionally, incentives received are treated as a reduction of costs over the term of the agreement, as they are considered an inseparable part of the lease agreement.

Comprehensive Income

Comprehensive income is defined as the change in stockholders’ equity of a business enterprise during a period from transactions and other events and circumstances from non‑owner sources. Comprehensive income consists of net income and other comprehensive income, which includes certain changes in equity that are excluded from net income. Specifically, cumulative foreign currency translation adjustments are included in accumulated other comprehensive income. As of December 31, 2018, 2017, and 2016, accumulated other comprehensive income is presented separately on the consolidated balance sheets and consists entirely of cumulative foreign currency translation adjustments.

Contingent Liabilities

The Company has certain contingent liabilities that arise in the ordinary course of business activities. The Company accrues for loss contingencies when losses become probable and are reasonably estimable. If the reasonable estimate of the loss is a range and no amount within the range is a better estimate, the minimum amount of the range is recorded as a liability. The Company does not accrue for contingent losses that, in its judgment, are considered to be reasonably possible, but not probable; however, it discloses the range of such reasonably possible losses.

Recent Accounting Pronouncements Not Yet Adopted

From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies and adopted by the Company on or prior to the specified effective date. Unless otherwise discussed, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on its financial position or results of operations upon adoption.

Leases

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”). ASU 2016-02 requires a lessee to recognize most leases on the balance sheet but recognize expenses on the income statement in a manner similar to current practice. The update states that a lessee will recognize a lease liability for the obligation to make lease payments and a right-to-use asset for the right to use the underlying assets for the lease term. Leases will continue to be classified as either financing or operating, with classification affecting the recognition, measurement, and presentation of expenses and cash flows arising from a lease. For certain public entities, including the Company, the new standard is effective for interim and annual periods beginning on or after January 1, 2019, with early adoption permitted. The Company will adopt this standard on January 1, 2019.

In July 2018, the FASB issued ASU No. 2018-11, Leases (Topic 842): Targeted Improvements (“ASU 2018-11”). ASU 2018-11 provides entities with an additional (and optional) transition method to adopt the new leases standard. Under this new transition method, an entity initially applies the new leases standard at the adoption date and recognizes a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption.

The Company plans to adopt ASU 2016-02 using the transition method allowed under ASU 2018-11. Upon adoption, the Company expects to elect the transition relief package, permitted within the standard, pursuant to which the Company will not reassess the classification of existing leases, whether any expired or existing contracts contain a lease, and whether existing leases have any initial direct costs. While the Company is still evaluating the impact that ASU 2016-02 may have on its consolidated financial statements, it anticipates that such guidance will materially impact its balance sheet given the Company’s leasing commitments as of December 31, 2018, as disclosed in Note 6.

Other Recent Accounting Pronouncements

In August 2018, the FASB issued ASU 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40) Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. This update aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. This new standard requires customers to expense the capitalized implementation costs over the term of the hosting arrangement. Amounts expensed would be presented through operating expense, rather than depreciation or amortization. Accounting for the service component of a hosting arrangement remains unchanged. The new standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted and an entity can elect to apply the new guidance on a prospective or retrospective basis. The Company is currently assessing the impact that adopting this guidance will have on its consolidated financial statements.

In June 2018, the FASB issued ASU No. 2018-07, Compensation—Stock Compensation (Topic 718) (“ASU 2018-07”). ASU 2018-07 expands the scope of Topic 718, Compensation—Stock Compensation, to include share-based payment transactions for acquiring goods and services from non-employees. The amendments in this update state that an entity should apply the requirements of Topic 718 to non-employee awards except for specific guidance on inputs to an option pricing model and the attribution of cost (that is, the period of time over which share-based payment awards vest and the pattern of cost recognition over that period). The amendments specify that Topic 718 applies to all share-based payment transactions in which a grantor acquires goods or services to be used or consumed in a grantor’s own operations by issuing share-based payment awards. The amendments also clarify that Topic 718 does not apply to share-based payments used to effectively provide (1) financing to the issuer or (2) awards granted in conjunction with selling goods or services to customers as part of a contract accounted for under Topic 606, Revenue from Contracts with Customers. The amendments in this update are effective for public business entities for fiscal years beginning after December 15, 2018, including interim periods within that fiscal year. For all other entities, the amendments are effective for fiscal years beginning after December 15, 2019, and interim periods within fiscal years beginning after December 15, 2020. Early adoption is permitted, but no earlier than an entity’s adoption date of Topic 606. The Company has assessed the impact of this guidance on its consolidated financial statements and does not deem it to be material. The Company plans to adopt the guidance on January 1, 2019.

In January 2017, the FASB issued ASU 2017-04, Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. The new guidance simplifies the accounting for goodwill impairment by eliminating Step 2 of the goodwill impairment test. Under current guidance, Step 2 of the goodwill impairment test requires entities to calculate the implied fair value of goodwill in the same manner as the amount of goodwill recognized in a business combination by assigning the fair value of a reporting unit to all of the assets and liabilities of the reporting unit. The carrying value in excess of the implied fair value is recognized as goodwill impairment. Under the new standard, goodwill impairment is recognized based on Step 1 of the current guidance, which calculates the carrying value in excess of the reporting unit’s fair value. The new standard is effective beginning in January 2020, with early adoption permitted. The Company will evaluate this guidance in connection with the purchase price allocation of the PistonHeads acquisition described in Note 14.

Fair Value of Financial Instruments Including Cash, Cash Equivalents and Investments

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments Including Cash, Cash Equivalents and Investments

3. Fair Value of Financial Instruments Including Cash, Cash Equivalents and Investments

ASC 820, Fair Value Measurements and Disclosures, establishes a three‑level valuation hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability, and are developed based on the best information available in the circumstances.

ASC 820 identifies fair value as the exchange price, or exit price, representing the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants based on the highest and best use of the asset or liability. As such, fair value is a market‑based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. The Company uses valuation techniques to measure fair value that maximize the use of observable inputs and minimize the use of unobservable inputs. These inputs are prioritized as follows:

Level 1 — Quoted unadjusted prices for identical instruments in active markets.

Level 2 — Quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model‑derived valuations in which all observable inputs and significant value drivers are observable in active markets.

Level 3 — Model‑derived valuations in which one or more significant inputs or significant value drivers are unobservable, including assumptions developed by the Company.

The valuation techniques that may be used to measure fair value are as follows:

Market Approach — Uses prices and other relevant information generated by market transactions involving identical or comparable assets or liabilities.

Income Approach — Uses valuation techniques to convert future amounts to a single present amount based on current market expectations about those future amounts, including present value techniques, option pricing models, and excess earnings method.

Cost Approach — Based on the amount that currently would be required to replace the service capacity of an asset (replacement cost).

The following tables present, for each of the fair value levels, the Company’s assets that are measured at fair value on a recurring basis at December 31, 2018 and 2017:

	December 31, 2018
	Quoted Prices in Active Markets for Identical Assets (Level 1 Inputs)		Significant Other Observable Inputs (Level 2 Inputs)		Significant Unobservable Inputs (Level 3 Inputs)		Total
Assets:
Cash equivalents:
Money market funds	$	24	$	—	$	—	$	24
Investments:
Certificates of deposit		—		122,800		—		122,800
Total	$	24	$	122,800	$	—	$	122,824

	December 31, 2017
	Quoted Prices in Active Markets for Identical Assets (Level 1 Inputs)		Significant Other Observable Inputs (Level 2 Inputs)		Significant Unobservable Inputs (Level 3 Inputs)		Total
Assets:
Cash equivalents:
Money market funds	$	60,709	$	—	$	—	$	60,709
Investments:
Certificates of deposit		—		50,000		—		50,000
Total	$	60,709	$	50,000	$	—	$	110,709

The Company measures eligible assets and liabilities at fair value with changes in value recognized in earnings. There were no liabilities that were measured at fair value for the years ended December 31, 2018 and 2017. Fair value treatment may be elected either upon initial recognition of an eligible asset or liability or, for an existing asset or liability, if an event triggers a new basis of accounting. The Company did not elect to remeasure any of its existing financial assets or liabilities and did not elect the fair value option for any financial assets and liabilities transacted in the years ended December 31, 2018 or 2017.

The following is a summary of cash, cash equivalents, and investments as of December 31, 2018 and 2017.

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
December 31, 2018:
Cash and cash equivalents due in 90 days or less	$	34,887	$	—	$	—	$	34,887
Investments:
Certificates of deposit due in one year or less		122,800		—		—		122,800
Total cash, cash equivalents, and investments	$	157,687	$	—	$	—	$	157,687

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
December 31, 2017:
Cash and cash equivalents due in 90 days or less	$	87,709	$	—	$	—	$	87,709
Investments:
Certificates of deposit due in one year or less		50,000		—		—		50,000
Total cash, cash equivalents, and investments	$	137,709	$	—	$	—	$	137,709

Property and Equipment, Net

12 Months Ended

Dec. 31, 2018

Property Plant And Equipment [Abstract]

Property and Equipment, Net

4. Property and Equipment, Net

Property and equipment consists of the following:

	At December 31,
	2018			2017
Computer equipment	$	4,208		$	3,532
Capitalized software		252			174
Website development costs		6,907			4,895
Furniture and fixtures		4,584			4,421
Leasehold improvements		10,821			10,797
Construction in progress		8,971			46
		35,743			23,865
Less accumulated depreciation		(11,474	)		(7,302	)
Property and equipment, net	$	24,269		$	16,563

Depreciation and amortization expense, which includes amortization expense associated with capitalized website and software development costs, was $5,029, $3,795, and $2,072 for the years ended December 31, 2018, 2017, and 2016, respectively. The increase of $8,925 in construction in progress at December 31, 2018 is primarily due to costs incurred to build out the Company’s new leased facility which was not occupied until subsequent to December 31, 2018.

Accrued Expenses, Accrued Income Taxes and Other Current Liabilities

12 Months Ended

Dec. 31, 2018

Accrued Liabilities Current [Abstract]

Accrued Expenses, Accrued Income Taxes and Other Current Liabilities

5. Accrued expenses, accrued income taxes and other current liabilities

Accrued expenses, accrued income taxes and other current liabilities consist of the following:

	At December 31,
	2018		2017
Accrued bonuses	$	8,266	$	7,807
Other accrued expenses, accrued income taxes and other current liabilities		10,388		5,781
	$	18,654	$	13,588

Commitments and Contingencies

12 Months Ended

Dec. 31, 2018

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

6. Commitments and Contingencies

Operating Leases

The Company leases its facilities under non‑cancelable operating leases with various expiration dates through October 2033. Rent expense for non-cancelable operating leases with free rental periods or scheduled rent increases is recognized on a straight-line basis over the terms of the leases. The difference between required lease payments and rent expense has been recorded as deferred rent.

On June 19, 2018, the Company entered into an operating lease in Cambridge, Massachusetts at 121 First St. for the lease of 48,393 square feet of office space with a non-cancellable lease term through 2033 with an option to extend the lease term for two additional periods of five years each.

On March 11, 2016, the Company entered into an operating lease in Cambridge, Massachusetts at 55 Cambridge Parkway for the lease of 51,923 square feet of office space with a non-cancellable lease term through 2024 with an option to extend the lease term for one additional period of five years.

On October 8, 2014, the Company entered into an operating lease in Cambridge, Massachusetts at 2 Canal Park for the lease of 48,059 square feet of office space with a non-cancellable lease term through 2022 with an option to extend the lease term for one additional period of five years.

Each of the three leases described above provides for leasehold improvement incentives and annual rent increases through the term of the lease.

As of December 31, 2018, the Company had deferred rent and rent incentives of $11,088, of which $1,693 and $9,395, respectively, are classified as a short‑term liability and a long‑term liability in the corresponding consolidated balance sheet. As of December 31, 2017, the Company had deferred rent and rent incentives of $6,813, of which $1,165 and $5,648, respectively, are classified as a short‑term liability and a long‑term liability in the corresponding consolidated balance sheet. Rent expense related to the operating leases for the years ended December 31, 2018, 2017, and 2016 was $7,711, $5,994, and $3,678 respectively.

Future minimum rental commitments under the Company’s operating leases at December 31, 2018 are as follows:

Year Ending December 31,	Operating Lease Commitments
2019	$	11,509
2020		11,077
2021		11,184
2022		10,878
2023 and thereafter		43,327
	$	87,975

Legal Matters

From time to time the Company may become involved in legal proceedings or be subject to claims arising in the ordinary course of its business. The Company is not presently subject to any pending or threatened litigation that it believes, if determined adversely to the Company, individually, or taken together, would reasonably be expected to have a material adverse effect on its business or financial results.

Guarantees and Indemnification Obligations

In the ordinary course of business, the Company enters into agreements with its customers that include commercial provisions with respect to licensing, infringement, indemnification, and other common provisions. The Company does not, in the ordinary course, agree to indemnification obligations for the Company under its contracts with customers. Based on historical experience and information known at December 31, 2018, 2017, and 2016, the Company has not incurred any costs for guarantees or indemnities.

Convertible Preferred Stock and Stockholders' Equity

12 Months Ended

Dec. 31, 2018

Equity [Abstract]

Convertible Preferred Stock and Stockholders' Equity

7. Convertible Preferred Stock and Stockholders’ Equity

On August 23, 2016, the Company completed a Series E convertible preferred stock, or Series E Preferred Stock, offering in the amount of $59,732, net of issuance costs of approximately $268. In connection with this issuance, the Company used the proceeds received to repurchase and retire certain outstanding shares of Series A, Series B, and Series C Preferred Stock and common stock, as well as certain vested stock options and restricted stock units from existing stockholders. The difference between the amount implicitly paid to repurchase the various classes of Preferred Stock and the corresponding carrying value of the underlying shares, or $32,087, was treated as a deemed dividend and was recorded against retained earnings. As the shares of common stock were repurchased for constructive retirement, the excess purchase price over the corresponding par value was charged directly to retained earnings.

On June 21, 2017, the Company amended and restated its Certificate of Incorporation pursuant to the Third Amended and Restated Certificate of Incorporation. Under the Third Amended and Restated Certificate of Incorporation, the total number of shares of all classes of stock which the Company had authority to issue was (i) 120,020,700 shares of Class A common stock, par value $0.001 per share, (ii) 80,013,800 shares of Class B common stock, par value $0.001 per share, and (iii) 11,091,782 shares of Preferred Stock, par value $0.001 per share, of which 3,333,000 shares were designated Series A Preferred Stock, 3,329,497 shares were designated Series B Preferred Stock, 1,648,978 shares were designated Series C Preferred Stock, 1,673,105 shares were designated Series D Preferred Stock, and 1,107,202 shares were designated Series E Preferred Stock. The Series A Preferred Stock, Series B Preferred Stock, Series C Preferred Stock, Series D Preferred Stock, and Series E Preferred Stock are referred to collectively as the Preferred Stock.

Upon the effectiveness of the Third Amended and Restated Certificate of Incorporation, (i) each share of Class A common stock issued and outstanding was recapitalized, reclassified, and reconstituted into two fully paid and non‑assessable shares of outstanding Class A common stock and four fully paid and non‑assessable shares of outstanding Class B common stock, and (ii) each share of Class B common stock of the Company issued and outstanding was recapitalized, reclassified, and reconstituted into two fully paid and non‑assessable shares of outstanding Class A common stock and four fully paid and non‑assessable shares of outstanding Class B common stock.

Further, upon the effectiveness of the Third Amended and Restated Certificate of Incorporation, the number of shares of common stock as to which each outstanding option to purchase common stock was exercisable for and each outstanding RSU was convertible into was adjusted such that upon exercise of outstanding stock options or vesting of outstanding RSUs, each holder would receive two fully paid and non‑assessable shares of Class A common stock and four fully paid and non‑assessable shares of Class B common stock in respect of each share of common stock previously underlying such option or RSU. The exercise price per share of common stock underlying each outstanding option was adjusted upon the effectiveness of the Third Amended and Restated Certificate of Incorporation to be one‑sixth of the exercise price per share in effect immediately prior to such adjustment and the fair market value per share of common stock issuable upon settlement of such RSU was adjusted to be one‑sixth of the fair market value per share in effect immediately prior to the recapitalization.

All share and per share data shown in the accompanying consolidated financial statements and related notes have been retroactively revised to reflect the share recapitalization.

On October 16, 2017, in connection with the closing of the IPO, all of the outstanding shares of Preferred Stock automatically converted into 20,188,226 shares of Class A common stock and 40,376,452 shares of Class B common stock. The 40,376,452 shares of Class B common stock subsequently converted into 40,376,452 shares of Class A common stock resulting in a total conversion of all outstanding shares of Preferred Stock into 60,564,678 shares of Class A common stock. Subsequent to the closing of the IPO, there were no shares of Preferred Stock outstanding.

Immediately following such conversion, the Company’s Fourth Amended and Restated Certificate of Incorporation became effective. Pursuant to the Fourth Amended and Restated Certificate of Incorporation, the Company is authorized to issue up to 500,000,000 shares of Class A common stock, 100,000,000 shares of Class B common stock, and 10,000,000 shares of Preferred Stock, all with a par value of $0.001 per share. As of December 31, 2018, the Preferred Stock is undesignated and no Preferred Stock is outstanding.

In addition, pursuant to the Fourth Amended and Restated Certificate of Incorporation, all shares of Class B common stock will automatically convert into shares of Class A common stock, on a share for share basis, upon the date falling after the first to occur of (1) the death of Langley Steinert, the Company’s Chief Executive Officer and Chairman, (2) his voluntary termination of all employment with the Company and service on the Company’s board of directors, or (3) the sum of the number of shares of capital stock held by Langley Steinert, by any Family Member of Langley Steinert, and by any Permitted Entity of Langley Steinert (as such terms are defined in the Fourth Amended and Restated Certificate of Incorporation), assuming the exercise and settlement in full of all outstanding options and convertible securities and calculated on an as-converted to Class A common stock basis, being less than 9,091,484. Shares of Class B common stock will not automatically convert into shares of Class A common stock upon the termination of Mr. Steinert's status as an officer and director, unless such termination is either made voluntarily by Mr. Steinert or due to Mr. Steinert's death. Once converted into Class A common stock, the converted shares of Class B common stock will not be reissued. In addition, if all shares of Class B common stock are converted into Class A common stock, then any outstanding options or convertible securities with the right to purchase or acquire shares of Class B common stock shall become a right to purchase or acquire shares of Class A common stock.

Common Stock

Each share of Class A common stock entitles the holder to one vote for each share on all matters submitted to a vote of the Company’s stockholders at all meetings of stockholders and written actions in lieu of meetings. Each share of Class B common stock entitles the holder to ten votes for each share on all matters submitted to a vote of the Company’s stockholders at all meetings of stockholders and written actions in lieu of meetings.

Holders of common stock are entitled to receive dividends, when and if declared by the Board.

At December 31, 2018, each share of Class B common stock was convertible into one share of Class A common stock at the option of the holder at any time. Automatic conversion of each share of Class B common stock will occur upon the occurrence of certain events, as described in the Fourth Amended and Restated Certificate of Incorporation.

Upon the effectiveness of the Company’s Fourth Amended and Restated Certificate of Incorporation, additional terms of conversion and transfer were implemented as discussed above.

Preferred Stock

Prior to the Company’s IPO, at which time all shares of Preferred Stock were converted into shares of common stock, the Company’s Preferred Stock consisted of the following:

	Original Issue Price Per Share		Shares Authorized		Outstanding		Liquidation Amount		Carrying Value
Series A Preferred Stock	$	0.525053		3,333,000		2,824,703	$	1,483	$	1,483
Series B Preferred Stock	$	0.780899		3,329,497		2,938,486		2,295		2,295
Series C Preferred Stock	$	0.849012		1,648,978		1,550,612		1,316		1,316
Series D Preferred Stock	$	40.642989		1,673,105		1,673,105		68,000		67,872
Series E Preferred Stock	$	54.190650		1,107,202		1,107,202		60,000		59,732
				11,091,782		10,094,108	$	133,094	$	132,698

The holders of the Company’s Preferred Stock had certain voting and dividend rights, as well as liquidation preferences and conversion privileges. All rights, preferences, and privileges associated with the Preferred Stock were terminated at the time of the Company’s IPO in conjunction with the conversion of all outstanding shares of Preferred Stock into shares of common stock.

Stock-based Compensation

12 Months Ended

Dec. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-based Compensation

8. Stock‑based Compensation

Equity Incentive Plans

The Company’s Amended and Restated 2006 Equity Incentive Plan (the “2006 Plan”) provided for the issuance of non-qualified stock options, restricted stock and stock awards to the Company’s employees, officers, directors and consultants. The 2006 Plan authorized up to an aggregate of 3,444,668 shares of the Company's Class B common stock for such issuances. In conjunction with the effectiveness of the Company’s 2015 Equity Incentive Plan (the “2015 Plan”), the Board voted that no further stock options or other equity-based awards may be granted under the 2006 Plan.

In 2015, the Board first adopted the 2015 Plan, which became effective on June 26, 2015. The 2015 Plan provided for the issuance of incentive stock options, non-qualified stock options, restricted stock, stock awards and restricted stock units (“RSUs”) to employees, consultants and non-employee directors. As of the effective date of the 2015 Plan, up to 603,436 shares of common stock were authorized for issuance under the 2015 Plan. The 2015 Plan was amended and restated effective August 6, 2015 to permit the granting of RSUs under the 2015 Plan, remove Class B common stock from the pool of shares available for issuance under the 2015 Plan and make certain other desired changes. The 2015 Plan was further amended and restated at October 15, 2015 to add a ten-year term and to make certain other desired changes.

The 2015 Plan was further amended and restated effective August 22, 2016 to merge the 2006 Plan into the 2015 Plan, to increase the number of shares of Class A common stock that may be issued under the 2015 Plan, and to lengthen the term of the 2015 Plan to expire on August 21, 2026. In addition, pursuant to this amendment and restatement of the 2015 Plan, prior to giving effect to the recapitalization that occurred on June 21, 2017, there were (i) 618,691 shares of Class A common stock, plus (ii) 802,562 shares of Class B common stock authorized under the 2015 Plan; provided, however, that (1) the number of shares of Class A common stock was increased, on a share for share basis, by the number of shares of Class B common stock that were (a) subject to outstanding options granted under the 2006 Plan that expired, terminated, or were cancelled for any reason without having been exercised, (b) surrendered in payment of the exercise price of outstanding options granted under the 2006 Plan or (c) withheld in satisfaction of tax withholding upon exercise of outstanding options granted under the 2006 Plan, and the number of shares of Class B common stock reserved under the amended and restated 2015 Plan was decreased, on a corresponding share for share basis, (2) no new awards of Class B common stock could be granted under the amended and restated 2015 Plan, and (3) except with respect to outstanding options granted under the 2006 Plan that were exercised on or after the date of the amendment and restatement, no Class B common stock could be issued under the 2015 Plan.

In connection with the recapitalization that occurred on June 21, 2017, the 2015 Plan was further amended and restated to account for each outstanding common stock option being adjusted such that each share of common stock underlying such option became two shares of Class A common stock and four shares of Class B common stock underlying such option, and each outstanding RSU being adjusted such that each share of common stock issuable upon settlement of such RSU became two shares of Class A common stock and four shares of Class B common stock issuable upon settlement of such RSU. Pursuant to the 2015 Plan as further amended in connection with the recapitalization, there were (i) 3,181,740 shares of Class A common stock and (ii) 5,161,644 shares of Class B common stock authorized for issuance under the 2015 Plan.

In connection with the IPO, in October 2017, the Board adopted, and the Company’s stockholders approved, the Omnibus Equity Compensation Plan (the “2017 Plan”) for the purpose of granting incentive stock options, non-qualified stock options, stock awards, stock units, other share-based awards and cash awards to employees, advisors and consultants to the Company and its subsidiaries and non-employee members of the Company’s board of directors. The 2017 Plan is the successor to the 2015 Plan. The 2017 Plan authorizes the issuance or transfer of the sum of: (i) 7,800,000 shares of the Company’s Class A common stock, plus (ii) the number of shares of our Class A common stock (up to 4,500,000 shares) equal to the sum of (x) the number of shares of Class A common stock and Class B common stock of the Company subject to outstanding awards under the 2015 Plan as of October 10, 2017 that terminate, expire or are cancelled, forfeited, exchanged, or surrendered on or after October 10, 2017 without having been exercised, vested, or paid prior to October 10, 2017, including shares tendered or withheld to satisfy tax withholding obligations with respect to outstanding grants under the Prior 2015 Plan, plus (y) the number of shares of Class A common stock reserved for issuance under the 2015 Plan that remain available for grant under the 2015 Plan as of the October 10, 2017. The aggregate number of shares of Class A common stock that may be issued or transferred under the 2017 Plan pursuant to incentive stock options will not exceed 12,300,000 shares of Class A common stock. Unless determined otherwise by the Compensation Committee of the Board, as of the first trading day of January of each calendar year during the term of the 2017 Plan (excluding any extensions), eligible beginning with calendar year 2019, an additional number of shares of Class A common stock will be added to the number of shares of the Company’s Class A common stock authorized to be issued or transferred under the 2017 Plan and the number of shares authorized to be issued or transferred pursuant to incentive stock options, equal to 4% of the total number of shares of our Class A common stock outstanding on the last trading day in December of the immediately preceding calendar year, or 6,000,000 shares, whichever is less, or such lesser amount as determined by the Board (the “Evergreen Increase”). The Compensation Committee of the Board determined to not effectuate the Evergreen Increase that was otherwise scheduled to have occurred on January 2, 2019. In conjunction with the adoption of the 2017 Plan, options and RSUs outstanding under the 2015 Plan will remain outstanding but no additional grants will be made from the 2015 Plan.

At December 31, 2018, 6,839,584 shares of Class A common stock were available for issuance under the 2017 Plan.

The following is a summary of the stock option activity for all stock‑based compensation plans during the year ended December 31, 2018:

	Common Stock			Weighted-Average Exercise Price for Equity		Weighted-Average Contractual Life (In Years)		Aggregate Intrinsic Value⁽¹⁾
Outstanding, December 31, 2017		5,041,540		$	1.60		6.0	$	143,059
Granted		—			—		—		—
Exercised		(3,197,179	)	1.14			—		111,227
Forfeited and cancelled		(36,846	)	5.47			—
Outstanding, December 31, 2018		1,807,515		$	2.35		5.9	$	56,716
Options exercisable at December 31, 2018		1,522,101		$	1.58	5.7		$	48,928

⁽¹⁾	The aggregate intrinsic value was calculated based on the positive difference, if any, between the estimated fair value of our common stock on December 31, 2018, 2017, and 2016 respectively, or the date of exercise, as appropriate, and the exercise price of the underlying options.

There were no options granted in the years ended December 31, 2018 and 2017. The weighted-average grant-date fair value of options granted was $0.90 per share in 2016.

The aggregate intrinsic value for options exercised during the years ended December 31, 2017 and 2016 was $2,238 and $2,021, respectively.

The following is a summary of the RSU activity during the year ended December 31, 2018:

	Number of Shares			Weighted- Average Grant Date Fair Value		Aggregate Intrinsic Value
Unvested outstanding, December 31, 2017		2,372,380		$	12.34	$	71,124
Granted		1,917,043		35.79
Vested		(1,087,279	)	14.71
Cancelled		(229,142	)	19.46
Unvested outstanding, December 31, 2018		2,973,002		$	26.06	$	100,279

The weighted-average grant-date fair value of RSUs granted was $16.99 and $3.89 per share in 2017 and 2016, respectively.

RSUs that vested and settled during the year ended December 31, 2018 totaled 1,781,201, which included 1,087,279 and 693,922 RSUs that vested in 2018 and 2017, respectively. RSUs that vested prior to April 10, 2018 did not settle until the expiration of shareholder lock-up agreements on such date.

The total fair value of RSUs vested was $15,994 and $2,505 in the years ended December 31, 2018 and 2017. No RSUs vested in the year ended December 31, 2016.

For the years ended December 31, 2018, 2017, and 2016, total stock‑based compensation expense was $20,794, $5,028, and $322, respectively. The following two tables show stock compensation expense by award type and where the stock compensation expense is recorded in the Company’s consolidated statements of operations:

	Year Ended December 31,
	2018		2017		2016
Options	$	247	$	281	$	322
RSUs		20,547		4,747		—
Total stock-based compensation	$	20,794	$	5,028	$	322

	Year Ended December 31,
	2018		2017		2016
Cost of revenue	$	354	$	151	$	18
Sales and marketing expense		5,111		1,911		163
Product, technology, and development expense		9,865		1,637		104
General and administrative expense		5,464		1,329		37
	$	20,794	$	5,028	$	322

Excluded from stock-based compensation expense is $490 and $176 of capitalized software development costs in 2018 and 2017, respectively. Stock-based compensation expense related to capitalized software development costs was immaterial in 2016.

The income tax benefit from stock-based compensation expense was $1,945, $1,301, and $67 in the years ended December 31, 2018, 2017, and 2016, respectively.

As of December 31, 2018, there was $186 of unrecognized stock‑based compensation expense related to unvested stock options, which is expected to be recognized over a weighted‑average period of 1.1 years.

As of December 31, 2018, there was $69,998 of unrecognized stock‑based compensation expense, related to unvested RSUs which is expected to be recognized over a weighted‑average period of 3.2 years.

Common Stock Reserved for Future Issuance

At December 31, 2018, the Company had reserved the following shares of voting common stock for future issuance:

Common stock options outstanding			1,807,515
Restricted stock units outstanding			2,973,002
Shares available for issuance under the 2017 Plan			6,839,584
Total shares of authorized common stock reserved for future issuance			11,620,101

Earnings Per Share

12 Months Ended

Dec. 31, 2018

Earnings Per Share [Abstract]

Earnings Per Share

9. Earnings Per Share

Net income per share for the year ended December 31, 2018 was computed by dividing net income by the weighted-average number of common shares outstanding during the reporting period. The Company computes the weighted-average number of common shares outstanding during the reporting period using the total number of shares of Class A common stock and Class B common stock outstanding as of the last day of the previous year end reporting period plus the weighted-average of any additional shares issued and outstanding during the reporting period.

Net income per share for the year ended December 31, 2017 and 2016 was computed using the two-class method, which includes the weighted‑average number of shares of common stock outstanding during the period and other securities that participate in dividends (a participating security). As of December 31, 2016, and for periods during the year ended December 31, 2017, the Company had convertible Preferred Stock outstanding. The Company considered the convertible Preferred Stock to be participating securities because they included rights to participate in dividends with the common stock. On October 16, 2017, in connection with the closing of the IPO, all of the outstanding shares of convertible Preferred Stock automatically converted into 20,188,226 shares of Class A common stock and 40,376,452 shares of Class B common stock, the latter of which subsequently converted in full into shares of Class A common stock. As a result, there were no shares of Preferred Stock outstanding at the closing of the IPO and the Company has not issued any new shares of Preferred Stock since such closing.

Under the two‑class method, basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted‑average number of shares of common stock outstanding during the period. Diluted net income (loss) per share attributable to common stockholders is computed using the more dilutive of (1) the two‑class method or (2) the if‑converted method. The Company allocated net income first to preferred stockholders based on dividend rights under the Company’s certificate of incorporation that was in effect prior to the closing of the IPO and then to preferred and common stockholders based on ownership interests. Net losses are not allocated to preferred stockholders as they do not have an obligation to share in the Company’s net losses.

The Company has two classes of common stock authorized: Class A common stock and Class B common stock. The rights of the holders of Class A and Class B common stock are identical, except with respect to voting and conversion. Each share of Class A common stock is entitled to one vote per share and each share of Class B common stock is entitled to ten votes per share. Each share of Class B common stock is convertible into one share of Class A common stock at the option of the holder at any time or automatically upon certain events described in the Company’s amended and restated certificate of incorporation, including on either the death or voluntary termination of the Company’s Chief Executive Officer. The Company allocates undistributed earnings attributable to common stock between the common stock classes on a one‑to‑one basis when computing net income (loss) per share. As a result, basic and diluted net income (loss) per share of Class A common stock and per share of Class B common stock are equivalent.

During the year ended December 31, 2018, holders of Class B common stock converted 7,534,710 shares of Class B common stock to Class A common stock.

Diluted net income (loss) per share gives effect to all potentially dilutive securities. Potential dilutive securities for the years ended December 31, 2018, 2017 and 2016 consist of shares of common stock issuable upon the exercise of stock options and shares of common stock issuable upon the vesting of RSUs. Potential dilutive securities for the years ended December 31, 2017 and 2016 also included shares of common stock issuable upon the conversion of the outstanding Preferred Stock. The dilutive effect of these common stock equivalents is reflected in diluted earnings per share by application of the treasury stock method.

For the year ended December 31, 2018, dilutive net income per share was calculated by dividing net income by the weighted-average number of shares of common stock outstanding during the period plus the dilutive impact of stock options and shares of common stock issuable upon the vesting of RSUs. For the year ended December 31, 2017, the two‑class method was used in the computation of diluted net income per share, which was equally as dilutive as the if-converted method. For the year ended December 31, 2016, the net loss attributable to common stockholders was divided by the weighted‑average number of shares of common stock outstanding during the period to calculate diluted earnings per share. The dilutive effect of common stock equivalents has been excluded from the calculation as their effect would have been anti‑dilutive due to the net losses incurred for the periods after including the effects of deemed dividends on the Preferred Stock.

The following table presents a reconciliation of the numerator and denominator used in the calculation of basic and diluted net income (loss) per share:

	Year Ended December 31,
	2018		2017			2016
Numerator:
Net income	$	65,170	$	13,199		$	6,497
Deemed dividend to preferred stockholders		—		—			(32,087	)
Net income attributable to participating securities		—		(6,098	)		—
Net income (loss) attributable to common stockholders — basic	$	65,170	$	7,101		$	(25,590	)
Net income	$	65,170	$	13,199		$	6,497
Deemed dividend to preferred stockholders		—		—			(32,087	)
Net income attributable to participating securities		—		(5,829	)		—
Net income (loss) attributable to common stockholders — diluted	$	65,170	$	7,370		$	(25,590	)
Denominator:
Weighted–average number of shares of common stock used in computing net income per share attributable to common stockholders — basic		108,833,028		55,835,265			44,138,922
Dilutive effect of share equivalents resulting from stock options		3,009,748		4,290,362			—
Dilutive effect of share equivalents resulting from unvested restricted stock units		1,521,936		511,957			—
Weighted–average number of shares of common stock used in computing net income per share — diluted		113,364,712		60,637,584			44,138,922
Net income (loss) per share attributable to common stockholders:
Basic	$	0.60	$	0.13		$	(0.58	)
Diluted		0.57		0.12			(0.58	)

The following potentially dilutive common stock equivalents have been excluded from the calculation of diluted weighted‑average shares outstanding for the years ended December 31, 2018, 2017, and 2016, as their effect would have been anti‑dilutive for the periods presented:

	Year Ended December 31,
	2018		2017		2016
Stock options outstanding		—		—		5,698,812
Restricted stock units outstanding		126,816		829		1,580,094
Convertible preferred stock		—		—		10,094,108

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income Taxes

10. Income Taxes

The domestic and foreign components of income before income taxes are as follows:

	Year Ended December 31,
	2018		2017		2016
United States	$	24,426	$	15,543	$	8,919
Foreign		1,058		294		26
Income before income taxes	$	25,484	$	15,837	$	8,945

The (benefit from) provision for income taxes contained the following components:

	Year Ended December 31,
	2018			2017			2016
Current (benefit) provision:
Federal	$	(860	)	$	3,262		$	1,440
State		92			431			223
Foreign		122			62			3
		(646	)		3,755			1,666
Deferred (benefit) provision:
Federal		(27,675	)		(755	)		880
State		(11,499	)		(343	)		(98	)
Foreign		134			(19	)		—
		(39,040	)		(1,117	)		782
Income tax (benefit) provision	$	(39,686	)	$	2,638		$	2,448

The Company's effective tax rate for the year ending December 31, 2018 is less than the U.S. federal statutory rate due to excess tax deductions related to stock-based compensation awards and federal and state research and development credits. The Company’s effective tax rates for the years ending December 31, 2017 and 2016 are less than the U.S. federal statutory rate primarily due to federal and state research and development credits, excess tax deductions related to stock-based compensation awards, and tax deductions for fees incurred during the IPO process.

	Year Ended December 31,
	2018			2017			2016
U.S. federal taxes at statutory rate		21.0	%		35.0	%		35.0	%
State taxes, net of federal benefit		(25.6	)		3.1			4.5
Nondeductible expenses		4.1			1.2			2.0
Tax deductible IPO costs		—			(9.3	)		—
Stock compensation		(127.2	)		(4.4	)		—
Foreign rate differential		(0.4	)		(0.4	)		(0.1	)
Credits		(28.4	)		(9.0	)		(15.0	)
Other		0.7			0.5			1.0
Total		(155.8	)%		16.7	%		27.4	%

The approximate income tax effect of each type of temporary difference and carryforward as of December 31, 2018 and 2017 is as follows:

	As of December 31,
	2018			2017
Deferred tax assets:
Net operating loss carryforwards	$	34,450		$	—
Credit carryforwards		6,562			166
Stock-based compensation		1,945			1,301
Landlord allowance on leasehold improvements		1,908			1,078
Deferred rent		873			583
Accruals and reserves		1,074			606
		46,812			3,734
Deferred tax liability:
Prepaid expenses		(931	)		—
Deferred commissions		(3,187	)		—
Unbilled revenue		(227	)		—
Fixed assets		(3,581	)		(2,909	)
		(7,926	)		(2,909	)
Net deferred tax assets	$	38,886		$	825

The Company uses the asset and liability method to account for income taxes in accordance with ASC 740, Income Taxes. Under this method, deferred income taxes are recognized for the future tax consequences of differences between the tax and financial accounting bases of assets and liabilities at each reporting period. Deferred income taxes are based on enacted tax laws and statutory tax rates applicable to the period in which these differences are expected to affect taxable income. A valuation allowance is established when necessary to reduce deferred tax assets to the amounts expected to be realized.

The Tax Cuts and Jobs Act (the “TCJA”) was enacted on December 22, 2017. Among other things, the TCJA reduces the U.S. federal corporate tax rate from 35% to 21%, requires companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax deferred, and creates new taxes on certain foreign sourced earnings. In the first nine months of 2018 and year ended December 31, 2017, the Company recorded provisional amounts for certain enactment-date effects of the TCJA by applying the guidance of Staff Accounting Bulletin 118 because the Company had not yet completed the enactment-date accounting for these effects. In the year ended December 31, 2018 and 2017, the Company recorded tax expense related to the enactment-date effects of the TCJA that included recording the one-time transition tax liability related to undistributed earnings of certain foreign subsidiaries that were not previously taxed, adjusting deferred tax assets and liabilities and electing to account for global intangible low-taxed income (“GILTI”) as a period expense. The changes to 2017 enactment-date provisional amounts increased the tax expense by $16 in 2018, which is included as a component of income tax expense from continuing operations.

The Company re-measured certain deferred tax assets and liabilities based on the rates at which they are anticipated to reverse in the future, which is generally 21%. The amount recorded related to the re-measurement of the Company’s deferred tax balance was a tax expense of $151, recognized in the year ended December 31, 2017. There were no additional expenses recognized in the year ended December 31, 2018 related to the remeasurement of deferred tax assets and liabilities.

The one-time transition tax is based on the Company’s total post-1986 earnings and profits (“E&P”) for which the Company has previously deferred from U.S. income taxes. As of December 31, 2017, the Company recorded a provisional amount for the one-time transition tax liability of $36 for its foreign subsidiaries, resulting in an increase of income tax provision of $36. As of December 31, 2018, the Company has completed its calculation of the total post-1986 foreign E&P for these foreign subsidiaries. The Company has recognized an additional $16 in its income tax expense for its one-time transition tax liability.

The TCJA subjects a U.S. shareholder to tax on GILTI earned by certain foreign subsidiaries. An entity can make an accounting policy election, per the FASB Staff Q&A, Topic 740, No. 5, Accounting for Global Intangible Low-Taxed Income, either to recognize deferred taxes for temporary basis differences expected to reverse as GILTI in future years or to provide for the tax expense related to GILTI in the year the tax is incurred as a period expense only. Because the Company was evaluating the provision of GILTI as of December 31, 2017, the Company recorded no GILTI-related deferred amounts in 2017. After further consideration in the current year, the Company has elected to account for GILTI as a period cost in the year the tax is incurred.

The Company has not provided a valuation allowance against its net deferred tax assets at December 31, 2018 and 2017. Based upon the level of historical U.S. earnings and future projections over the period in which the net deferred tax assets are deductible, at this time, management believes it is more likely than not that the Company will realize the benefits of these deductible differences.

As of December 31, 2018, the Company has federal and state net operating loss carryforwards of $130,927 and $111,234, respectively. The federal net operating losses carryforward indefinitely, subject to an annual limitation of 80% of taxable income. The state net operating losses, excluding Florida and Georgia which carryforward indefinitely, expire at various dates beginning in 2028. As of December 31, 2018, the Company has federal and state tax credit carryforwards of $3,875 and $3,401, respectively, available to reduce future tax liabilities that expire at various dates through 2038. Utilization of the net operating losses and tax credit carryforwards, respectively, may be subject to an annual limitation due to ownership change limitations that have occurred previously or that could occur in the future, as provided by Section 382 of the Code, or Section 382, as well as similar state provisions. Ownership changes may limit the amount of net operating losses or tax credit carryforwards that can be utilized annually to offset future taxable income and tax, respectively. In general, an ownership change, as defined by Section 382, results from transactions that increase the ownership of 5% stockholders in the stock of a corporation by more than 50% in the aggregate over a three-year period.

The Company previously adopted the provision for uncertain tax positions under ASC 740. The adoption did not have an impact on the Company’s retained earnings balance. At December 31, 2018 and 2017, the Company had no recorded liabilities for uncertain tax positions and had no accrued interest or penalties related to uncertain tax positions

The Company permanently reinvests the earnings, if any, of its foreign subsidiaries and, therefore, does not provide for U.S. income taxes that could results from the distribution of those earnings to the U.S. parent. As of December 31, 2018, the amount of unrecognized deferred U.S. taxes on these earnings would be de minimis.

The Company and its subsidiaries are subject to various U.S. federal, state, and foreign income taxes. The Company is currently not subject to examination under the statute of limitations by the Internal Revenue Service and state jurisdictions for the tax years of 2014 and prior. In 2018, the Internal Revenue Service commenced a federal income tax audit with respect to our 2016 tax year. The Company is also currently open to examination in its foreign jurisdictions for tax years 2016 and after.

Segment and Geographic Information

12 Months Ended

Dec. 31, 2018

Segment Reporting [Abstract]

Segment and Geographic Information

11. Segment and Geographic Information

The Company has two reportable segments, United States and International. Segment information is presented in the same manner as the Company’s chief operating decision maker, or CODM, reviews the Company’s operating results in assessing performance and allocating resources. The CODM reviews revenue and operating income (loss) for each reportable segment as a proxy for the operating performance of the Company’s United States and International operations. The Company’s chief executive officer is the CODM on behalf of both reportable segments.

The United States segment derives revenues from marketplace subscriptions, advertising services, and other revenues from customers within the United States. The International segment derives revenues from marketplace subscriptions, advertising services, and other revenues from customers outside of the United States. A majority of our operational overhead expenses, including technology and personnel costs, and other general and administrative costs associated with running our business, are incurred in the United States and not allocated to the International segment. Assets and costs discretely incurred by reportable segments, including depreciation and amortization, are included in the calculation of reportable segment income (loss) from operations. Segment operating income (loss) does not reflect the transfer pricing adjustments related to the Company’s foreign subsidiaries, which are recorded for statutory reporting purposes. Asset information is assessed and reviewed on a global basis.

Information regarding the Company’s operations by segment and geographical area is presented below:

	Year Ended December 31,
	2018⁽¹⁾		2017		2016
Segment revenue:
United States	$	437,166	$	307,472	$	195,824
International		16,920		9,389		2,317
Total revenue	$	454,086	$	316,861	$	198,141

	Year Ended December 31,
	2018⁽¹⁾			2017			2016
Segment income (loss) from operations:
United States	$	58,387		$	41,586		$	27,461
International		(35,196	)		(26,312	)		(18,890	)
Total income from operations	$	23,191		$	15,274		$	8,571

⁽¹⁾	Included in the year ended December 31, 2018 United States and International segments are revenue adjustments of $94 and $32, respectively, and operating income adjustments of $8,613 and $811, respectively, related to the Company's adoption of ASC 606.

As of December 31, 2018 and 2017, property and equipment held outside the United States was not material. Total assets in the United States segment account for 97% of the total consolidated assets.

Employee Benefit Plans

12 Months Ended

Dec. 31, 2018

Compensation And Retirement Disclosure [Abstract]

Employee Benefit Plans

12. Employee Benefit Plans

The Company maintains a defined contribution savings plan for all eligible U.S. employees under Section 401(k) of the Code. Effective July 1, 2017, the Company implemented a matching policy, under which the Company matches 50% of an employee’s annual contributions to the 401(k) plan, up to a maximum of the lesser of (i) 6% of the employee’s base salary, bonus and commissions paid during the year or (ii) $5,000. Matching contributions are subject to vesting based on the employee’s start date and length of service. Employees can designate the investment of their 401(k) accounts into several mutual funds. The Company does not allow investment in its common stock through the 401(k) plan.

During the year ended December 31, 2016, the Company did not make any employer contributions to the plan. During the year ended December 31, 2017, the Company began matching employee 401(k) contributions up to a set limit. Total employer contributions were $1,953 and $724 during the years ended December 31, 2018 and December 31, 2017, respectively.

Quarterly Financial Results (Unaudited)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Data [Abstract]

Quarterly Financial Results (unaudited)

13. Quarterly Financial Results (unaudited)

The following table presents certain unaudited quarterly financial information for the eight quarters in the period ended December 31, 2018. This information has been prepared on the same basis as the audited financial statements and includes all adjustments (consisting only of normal recurring adjustments) necessary to present fairly the unaudited quarterly results of operations set forth herein.

	Fourth Quarter		Third Quarter⁽¹⁾		Second Quarter⁽¹⁾		First Quarter⁽¹⁾
Year ended December 31, 2018
Revenue	$	126,090	$	119,125	$	110,296	$	98,575
Cost of revenue		6,871		6,412		5,959		5,569
Gross profit		119,219		112,713		104,337		93,006
Income from operations		6,902		5,877		3,953		6,459
Net income		12,450		13,882		33,343		5,495
Basic net income per share⁽¹⁾	$	0.11	$	0.13	$	0.31	$	0.05
Diluted net income per share ⁽¹⁾	$	0.11	$	0.12	$	0.29	$	0.05
Year ended December 31, 2017
Revenue	$	90,597	$	82,989	$	76,240	$	67,035
Cost of revenue		5,242		4,720		4,322		3,325
Gross profit		85,355		78,269		71,918		63,710
Income from operations		32		2,863		5,995		6,384
Net income		2,267		2,379		4,346		4,207
Basic net income per share⁽¹⁾	$	0.02	$	0.02	$	0.04	$	0.04
Diluted net income per share ⁽¹⁾	$	0.02	$	0.02	$	0.04	$	0.04

⁽¹⁾	The amounts were computed independently for each quarter, and the sum of the quarters may not total the annual amounts.

⁽²⁾	The amounts for the three months ended March 31, 2018, June 30, 2018 and September 30, 2018 were adjusted from previously reported amounts as a result of the adoption of ASC 606. Refer to the tables below for a reconciliation of the previously reported amounts to the adjusted amounts.

	First Quarter
	As Reported		ASC 606 Adjustment			As Adjusted
Three Months ended March 31, 2018
Revenue	$	98,701	$	(126	)	$	98,575
Cost of revenue		5,569		—			5,569
Gross profit		93,132		(126	)		93,006
Income from operations		3,922		2,537			6,459
Net income		3,651		1,844			5,495
Basic net income per share	$	0.03	$	0.02		$	0.05
Diluted net income per share	$	0.03	$	0.02		$	0.05

	Second Quarter
	As Reported		ASC 606 Adjustment			As Adjusted
Three Months ended June 30, 2018
Revenue	$	110,325	$	(29	)	$	110,296
Cost of revenue		5,959		—			5,959
Gross profit		104,366		(29	)		104,337
Income from operations		1,444		2,509			3,953
Net income		31,265		2,078			33,343
Basic net income per share	$	0.29	$	0.02		$	0.31
Diluted net income per share	$	0.28	$	0.01		$	0.29

	Third Quarter
	As Reported		ASC 606 Adjustment		As Adjusted
Three Months ended September 30, 2018
Revenue	$	119,042	$	83	$	119,125
Cost of revenue		6,412		—		6,412
Gross profit		112,630		83		112,713
Income from operations		3,635		2,242		5,877
Net income		12,135		1,747		13,882
Basic net income per share	$	0.11	$	0.02	$	0.13
Diluted net income per share	$	0.11	$	0.01	$	0.12

Subsequent Event

12 Months Ended

Dec. 31, 2018

Subsequent Events [Abstract]

Subsequent Event

14. Subsequent Event

On January 8, 2019, the Company, through CarGurus UK Limited, a company incorporated in England & Wales and a wholly owned subsidiary of CarGurus Ireland Limited (a company incorporated in Ireland and a wholly owned subsidiary of the Company) (the “Purchaser”), completed its acquisition of PistonHeads, a UK-based automotive website (“PistonHeads”), by acquiring the entire issued share capital of Haymarket New4 Ltd. (a company incorporated in England & Wales and now known as PistonHeads Holdco Limited, “NewCo”) from Haymarket Media Group Ltd., a company incorporated in England & Wales (the “Seller”), on the terms and subject to the conditions set forth in the Put and Call Option Agreement dated December 3, 2018, by and among the Purchaser, the Seller and Haymarket Group Limited, a company incorporated in England & Wales. The PistonHeads website hosts used car classifieds, articles and forums. The Company paid an aggregate of 15,000 GPB, or approximately $19,139, to acquire the business, inclusive of 1,000 GBP, or approximately $1,276, that will be held in escrow to secure post-closing claims, subject to the terms and conditions of an escrow agreement between Purchaser and Seller. Upon completion of the acquisition, NewCo became a wholly owned subsidiary of Purchaser. The business combination is intended to expand the Company’s consumer audience in the UK. During the year ended December 31, 2018, the Company incurred total acquisition-related costs of $452 related to the transaction. As the transaction occurred subsequent to period-end, the Company is still evaluating the purchase price allocation of the transaction but expects the primary assets acquired to be intangible assets and goodwill. Acquired tangible assets and assumed liabilities are expected to be immaterial. The allocation is expected to be finalized during the first half of 2019.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Basis of Presentation

Principles of Consolidation

Use of Estimates

Subsequent Events Considerations

Revenue Recognition

Marketplace Subscription Revenue

Customers do not have the right to take possession of the Company’s software.

Advertising and Other Revenue

Customers are billed monthly in arrears and payment terms are generally thirty to sixty days from the date invoiced.

Prior to adoption of ASC 606

Post adoption of ASC 606

Identify the contract with a customer

Identify the performance obligations in the contract

Determine the transaction price

Allocate the transaction price to performance obligations in the contract

Recognize revenue when or as the Company satisfies a performance obligation

Disaggregation of Revenue

The following table summarizes revenue from contracts with customers by revenue source for the year ended December 31, 2018.

	Year Ended
	December 31, 2018
Revenue by Revenue Stream
Marketplace subscription revenue	$	405,780
Advertising and other revenue		48,306
Total	$	454,086

Marketplace Subscription Revenue

Advertising and Other Revenue

For advertising revenue, the performance obligation is to publish the agreed upon campaign on the Company’s websites and load the related impressions.

As consideration is driven by the number of impressions delivered on the CarGurus websites, the consideration for each period is allocated to the period in which the service was rendered.

For other revenue, performance obligations are satisfied over time as services are rendered and revenue is recognized as it is earned.

Contracts with Multiple Performance Obligations

Costs to Obtain a Contract

Financial Statement Impact of Adopting ASC 606

	As Reported			Adjustments						As Adjusted
	December 31, 2017			Marketplace Subscription Revenue			Costs to Obtain a Contract			January 1, 2018
Assets
Current assets:
Cash and cash equivalents	$	87,709								$	87,709
Investments		50,000									50,000
Accounts receivable, net		12,577			813						13,390
Prepaid expenses and prepaid income taxes		5,313									5,313
Deferred contract costs		—						1,424			1,424
Other current assets		1,605									1,605
Restricted cash		—									—
Total current assets		157,204			813			1,424			159,441
Property and equipment, net		16,563									16,563
Restricted cash		1,843									1,843
Deferred tax assets		825			(190	)		(635	)		—
Deferred contract costs, net of current portion		—						1,783			1,783
Other long–term assets		159									159
Total assets	$	176,594		$	623		$	2,572		$	179,789
Liabilities and stockholders’ equity
Current liabilities:
Accounts payable	$	23,908								$	23,908
Accrued expenses, accrued income taxes and other current liabilities		13,588									13,588
Deferred revenue		4,305									4,305
Deferred tax liabilities		—						153			153
Deferred rent		1,165									1,165
Total current liabilities		42,966			—			153			43,119
Deferred rent, net of current portion		5,648									5,648
Other non–current liabilities		955									955
Total liabilities		49,569			—			153			49,722
Commitments and contingencies
Stockholders’ equity:
Preferred stock		—									—
Class A common stock		78									78
Class B common stock		28									28
Additional paid–in capital		185,190									185,190
Accumulated deficit		(58,499	)		623			2,419			(55,457	)
Accumulated other comprehensive income		228									228
Total stockholders’ equity		127,025			623			2,419			130,067
Total liabilities and stockholders’ equity	$	176,594		$	623		$	2,572		$	179,789

Marketplace Subscription Revenue

Costs to Obtain a Contract

Income Taxes

Impact of New Revenue Guidance on Financial Statement Line Items

	As of December 31, 2018
Balance Sheet	As Reported		Marketplace Subscription Revenue			Costs to Obtain a Contract			Pro forma as if the previous accounting guidance was in effect
Assets
Current assets:
Cash and cash equivalents	$	34,887							$	34,887
Investments		122,800								122,800
Accounts receivable, net		13,614		939						12,675
Prepaid income taxes and prepaid income taxes		10,144								10,144
Deferred contract costs		5,253					5,253			—
Other current assets		7,410								7,410
Restricted cash		750								750
Total current assets		194,858		939			5,253			188,666
Property and equipment, net		24,269								24,269
Restricted cash		1,921								1,921
Deferred tax assets		38,886		(227	)		(3,187	)		42,300
Deferred contract costs, net of current portion		7,252					7,252			—
Other long–term assets		1,104								1,104
Total assets	$	268,290	$	712		$	9,318		$	258,260
Liabilities and stockholders’ equity
Current liabilities:
Accounts payable	$	34,345							$	34,345
Accrued expenses, accrued income taxes and other current liabilities		18,654								18,654
Deferred revenue		8,811								8,811
Deferred rent		1,693								1,693
Total current liabilities		63,503		—			—			63,503
Deferred rent, net of current portion		9,395								9,395
Other non–current liabilities		1,281								1,281
Total liabilities		74,179		—			—			74,179
Commitments and contingencies
Stockholders’ equity:
Preferred stock		—								—
Class A common stock		90								90
Class B common stock		21								21
Additional paid–in capital		184,216								184,216
Retained earnings (accumulated deficit)		9,713		712			9,318			(317	)
Accumulated other comprehensive income		71								71
Total stockholders’ equity		194,111		712			9,318			184,081
Total liabilities and stockholders’ equity	$	268,290	$	712		$	9,318		$	258,260

There were no changes to liabilities as of December 31, 2018 as a result of the adoption of ASC 606.

	Year Ended December 31, 2018
Statement of Operations	As Reported			Marketplace Subscription Revenue		Costs to Obtain a Contract			Pro forma as if the previous accounting guidance was in effect
Revenue	$	454,086		$	126				$	453,960
Cost of revenue		24,811								24,811
Gross profit		429,275			126		—			429,149
Operating expenses:
Sales and marketing		315,939					(9,298	)		325,237
Product, technology, and development		47,866								47,866
General and administrative		39,475								39,475
Depreciation and amortization		2,804								2,804
Total operating expenses		406,084			—		(9,298	)		415,382
Income from operations		23,191			126		9,298			13,767
Other income, net:
Interest income		2,283								2,283
Other income (expense)		10								10
Total other income, net		2,293			—		—			2,293
Income before income taxes		25,484			126		9,298			16,060
(Benefit from) provision for income taxes		(39,686	)		37		2,399			(42,122	)
Net income	$	65,170		$	89	$	6,899		$	58,182
Basic	$	0.60		$	—	$	0.07		$	0.53
Diluted	$	0.57		$	—	$	0.06		$	0.51

	Year Ended December 31, 2018
Statement of Cash Flows	As Reported			Marketplace Subscription Revenue			Costs to Obtain a Contract			Pro forma as if the previous accounting guidance was in effect
Operating Activities
Net income	$	65,170		$	89		$	6,899		$	58,182
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		5,029									5,029
Unrealized currency (gain) loss on foreign denominated transactions		(190	)								(190	)
Deferred taxes		(39,040	)		37			2,399			(41,476	)
Provision for doubtful accounts		1,680									1,680
Stock–based compensation expense		20,794									20,794
Amortization of deferred contract costs		3,689						3,689			—
Changes in operating assets and liabilities:
Accounts receivable, net		(1,911	)		(126	)					(1,785	)
Prepaid expenses, prepaid income taxes, and other assets		(11,753	)								(11,753	)
Deferred contracts costs		(12,987	)					(12,987	)		—
Accounts payable		9,345									9,345
Accrued expenses, accrued income taxes and other current liabilities		2,695									2,695
Deferred revenue		4,508									4,508
Deferred rent		4,289									4,289
Other non–current liabilities		405									405
Net cash provided by operating activities		51,723			—			—			51,723

The following summarizes the opening and closing balances of receivables and contract assets from contracts with customers.

Accounts

Receivable, net

Contract Assets

(current)

Contract Assets

(non-current)

Balance at January 1, 2018

13,390

1,424

1,783

Balance at December 31, 2018

13,614

5,253

7,252

Transaction Price Allocated to Future Performance Obligations

Deferred Revenue

Cost of Revenue

Concentration of Credit Risk

For the years ended December 31, 2018, 2017 and 2016, no individual customer accounted for more than 10% of total revenue.

Cash, Cash Equivalents, and Investments

Restricted Cash

Accounts Receivable and Allowance for Doubtful Accounts

Unbilled accounts receivables are recorded for services rendered in the current period, but not invoiced until the subsequent period.

Below is a summary of the changes in the Company’s allowance for doubtful accounts for the years ended December 31, 2018, 2017, and 2016:

	Balance at Beginning of Period		Provision		Write–offs, net of recoveries			Balance at End of Period
Year ended December 31, 2018	$	494	$	1,680	$	(1,695	)	$	479
Year ended December 31, 2017		164		1,117		(787	)		494
Year ended December 31, 2016		75		508		(419	)		164

Property and Equipment

	Estimated Useful Life (In Years)
Computer equipment	3
Capitalized software	3
Website development costs	3
Furniture and fixtures	5
Leasehold improvements	Lesser of asset life or lease term

Foreign Currency Translation

Capitalized Website and Software Development Costs

Impairment of Long-Lived Assets

Impairment of Long‑Lived Assets

For the years ended December 31, 2018, 2017, and 2016, the Company did not identify any impairment of its long‑lived assets.

Income Taxes

Disclosure of Fair Value of Financial Instruments

Level 1 — Quoted unadjusted prices for identical instruments in active markets.

Level 3 — Model‑derived valuations in which one or more significant inputs or significant value drivers are unobservable, including assumptions developed by the Company.

The valuation techniques that may be used to measure fair value are as follows:

Market Approach — Uses prices and other relevant information generated by market transactions involving identical or comparable assets or liabilities.

Cost Approach — Based on the amount that currently would be required to replace the service capacity of an asset (replacement cost).

Stock-Based Compensation

Stock‑Based Compensation

The Company issues shares for stock option exercises and RSUs out of its shares available for issuance.

	2016
Expected dividend yield		—
Expected volatility		49	%
Risk–free interest rate		1.57	%
Expected term (in years)		6.07

See Note 8 for a summary of the stock option and RSU activity for the year ended December 31, 2018.

Advertising Costs

Leases

Comprehensive Income

Contingent Liabilities

Recent Accounting Pronouncements Not Yet Adopted

Leases

Other Recent Accounting Pronouncements

Earnings Per Share

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Summary of Opening and Closing Balances of Receivables and Contract Assets From Contracts with Customers

The following summarizes the opening and closing balances of receivables and contract assets from contracts with customers.

Accounts

Receivable, net

Contract Assets

(current)

Contract Assets

(non-current)

Balance at January 1, 2018

13,390

1,424

1,783

Balance at December 31, 2018

13,614

5,253

7,252

Summary of Changes in Allowance for Doubtful Accounts

Below is a summary of the changes in the Company’s allowance for doubtful accounts for the years ended December 31, 2018, 2017, and 2016:

	Balance at Beginning of Period		Provision		Write–offs, net of recoveries			Balance at End of Period
Year ended December 31, 2018	$	494	$	1,680	$	(1,695	)	$	479
Year ended December 31, 2017		164		1,117		(787	)		494
Year ended December 31, 2016		75		508		(419	)		164

Schedule of Estimated Useful Lives of Property and Equipment

The estimated useful lives of the Company’s property and equipment are as follows:

	Estimated Useful Life (In Years)
Computer equipment	3
Capitalized software	3
Website development costs	3
Furniture and fixtures	5
Leasehold improvements	Lesser of asset life or lease term

Schedule of Weighted-Average Assumptions Utilized to Determine Fair Value of Options Granted

The weighted‑average assumptions utilized to determine the fair value of options granted are presented in the following table:

	2016
Expected dividend yield		—
Expected volatility		49	%
Risk–free interest rate		1.57	%
Expected term (in years)		6.07

ASC 606

Summary of Revenue from Contracts With Customers by Revenue

The following table summarizes revenue from contracts with customers by revenue source for the year ended December 31, 2018.

	Year Ended
	December 31, 2018
Revenue by Revenue Stream
Marketplace subscription revenue	$	405,780
Advertising and other revenue		48,306
Total	$	454,086

Summary of Impact of New Revenue Guidance on Financial Statement

As a result of applying the modified retrospective method to adopt the new revenue guidance, the following adjustments were made on the consolidated balance sheet as of January 1, 2018.

	As Reported			Adjustments						As Adjusted
	December 31, 2017			Marketplace Subscription Revenue			Costs to Obtain a Contract			January 1, 2018
Assets
Current assets:
Cash and cash equivalents	$	87,709								$	87,709
Investments		50,000									50,000
Accounts receivable, net		12,577			813						13,390
Prepaid expenses and prepaid income taxes		5,313									5,313
Deferred contract costs		—						1,424			1,424
Other current assets		1,605									1,605
Restricted cash		—									—
Total current assets		157,204			813			1,424			159,441
Property and equipment, net		16,563									16,563
Restricted cash		1,843									1,843
Deferred tax assets		825			(190	)		(635	)		—
Deferred contract costs, net of current portion		—						1,783			1,783
Other long–term assets		159									159
Total assets	$	176,594		$	623		$	2,572		$	179,789
Liabilities and stockholders’ equity
Current liabilities:
Accounts payable	$	23,908								$	23,908
Accrued expenses, accrued income taxes and other current liabilities		13,588									13,588
Deferred revenue		4,305									4,305
Deferred tax liabilities		—						153			153
Deferred rent		1,165									1,165
Total current liabilities		42,966			—			153			43,119
Deferred rent, net of current portion		5,648									5,648
Other non–current liabilities		955									955
Total liabilities		49,569			—			153			49,722
Commitments and contingencies
Stockholders’ equity:
Preferred stock		—									—
Class A common stock		78									78
Class B common stock		28									28
Additional paid–in capital		185,190									185,190
Accumulated deficit		(58,499	)		623			2,419			(55,457	)
Accumulated other comprehensive income		228									228
Total stockholders’ equity		127,025			623			2,419			130,067
Total liabilities and stockholders’ equity	$	176,594		$	623		$	2,572		$	179,789

	As of December 31, 2018
Balance Sheet	As Reported		Marketplace Subscription Revenue			Costs to Obtain a Contract			Pro forma as if the previous accounting guidance was in effect
Assets
Current assets:
Cash and cash equivalents	$	34,887							$	34,887
Investments		122,800								122,800
Accounts receivable, net		13,614		939						12,675
Prepaid income taxes and prepaid income taxes		10,144								10,144
Deferred contract costs		5,253					5,253			—
Other current assets		7,410								7,410
Restricted cash		750								750
Total current assets		194,858		939			5,253			188,666
Property and equipment, net		24,269								24,269
Restricted cash		1,921								1,921
Deferred tax assets		38,886		(227	)		(3,187	)		42,300
Deferred contract costs, net of current portion		7,252					7,252			—
Other long–term assets		1,104								1,104
Total assets	$	268,290	$	712		$	9,318		$	258,260
Liabilities and stockholders’ equity
Current liabilities:
Accounts payable	$	34,345							$	34,345
Accrued expenses, accrued income taxes and other current liabilities		18,654								18,654
Deferred revenue		8,811								8,811
Deferred rent		1,693								1,693
Total current liabilities		63,503		—			—			63,503
Deferred rent, net of current portion		9,395								9,395
Other non–current liabilities		1,281								1,281
Total liabilities		74,179		—			—			74,179
Commitments and contingencies
Stockholders’ equity:
Preferred stock		—								—
Class A common stock		90								90
Class B common stock		21								21
Additional paid–in capital		184,216								184,216
Retained earnings (accumulated deficit)		9,713		712			9,318			(317	)
Accumulated other comprehensive income		71								71
Total stockholders’ equity		194,111		712			9,318			184,081
Total liabilities and stockholders’ equity	$	268,290	$	712		$	9,318		$	258,260

	Year Ended December 31, 2018
Statement of Operations	As Reported			Marketplace Subscription Revenue		Costs to Obtain a Contract			Pro forma as if the previous accounting guidance was in effect
Revenue	$	454,086		$	126				$	453,960
Cost of revenue		24,811								24,811
Gross profit		429,275			126		—			429,149
Operating expenses:
Sales and marketing		315,939					(9,298	)		325,237
Product, technology, and development		47,866								47,866
General and administrative		39,475								39,475
Depreciation and amortization		2,804								2,804
Total operating expenses		406,084			—		(9,298	)		415,382
Income from operations		23,191			126		9,298			13,767
Other income, net:
Interest income		2,283								2,283
Other income (expense)		10								10
Total other income, net		2,293			—		—			2,293
Income before income taxes		25,484			126		9,298			16,060
(Benefit from) provision for income taxes		(39,686	)		37		2,399			(42,122	)
Net income	$	65,170		$	89	$	6,899		$	58,182
Basic	$	0.60		$	—	$	0.07		$	0.53
Diluted	$	0.57		$	—	$	0.06		$	0.51

	Year Ended December 31, 2018
Statement of Cash Flows	As Reported			Marketplace Subscription Revenue			Costs to Obtain a Contract			Pro forma as if the previous accounting guidance was in effect
Operating Activities
Net income	$	65,170		$	89		$	6,899		$	58,182
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		5,029									5,029
Unrealized currency (gain) loss on foreign denominated transactions		(190	)								(190	)
Deferred taxes		(39,040	)		37			2,399			(41,476	)
Provision for doubtful accounts		1,680									1,680
Stock–based compensation expense		20,794									20,794
Amortization of deferred contract costs		3,689						3,689			—
Changes in operating assets and liabilities:
Accounts receivable, net		(1,911	)		(126	)					(1,785	)
Prepaid expenses, prepaid income taxes, and other assets		(11,753	)								(11,753	)
Deferred contracts costs		(12,987	)					(12,987	)		—
Accounts payable		9,345									9,345
Accrued expenses, accrued income taxes and other current liabilities		2,695									2,695
Deferred revenue		4,508									4,508
Deferred rent		4,289									4,289
Other non–current liabilities		405									405
Net cash provided by operating activities		51,723			—			—			51,723

Fair Value of Financial Instruments Including Cash, Cash Equivalents and Investments (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Schedule of Fair Value Levels, Assets Measured at Fair Value on Recurring Basis

The following tables present, for each of the fair value levels, the Company’s assets that are measured at fair value on a recurring basis at December 31, 2018 and 2017:

	December 31, 2018
	Quoted Prices in Active Markets for Identical Assets (Level 1 Inputs)		Significant Other Observable Inputs (Level 2 Inputs)		Significant Unobservable Inputs (Level 3 Inputs)		Total
Assets:
Cash equivalents:
Money market funds	$	24	$	—	$	—	$	24
Investments:
Certificates of deposit		—		122,800		—		122,800
Total	$	24	$	122,800	$	—	$	122,824

	December 31, 2017
	Quoted Prices in Active Markets for Identical Assets (Level 1 Inputs)		Significant Other Observable Inputs (Level 2 Inputs)		Significant Unobservable Inputs (Level 3 Inputs)		Total
Assets:
Cash equivalents:
Money market funds	$	60,709	$	—	$	—	$	60,709
Investments:
Certificates of deposit		—		50,000		—		50,000
Total	$	60,709	$	50,000	$	—	$	110,709

Schedule of Cash, Cash Equivalents, and Investments

The following is a summary of cash, cash equivalents, and investments as of December 31, 2018 and 2017.

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
December 31, 2018:
Cash and cash equivalents due in 90 days or less	$	34,887	$	—	$	—	$	34,887
Investments:
Certificates of deposit due in one year or less		122,800		—		—		122,800
Total cash, cash equivalents, and investments	$	157,687	$	—	$	—	$	157,687

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
December 31, 2017:
Cash and cash equivalents due in 90 days or less	$	87,709	$	—	$	—	$	87,709
Investments:
Certificates of deposit due in one year or less		50,000		—		—		50,000
Total cash, cash equivalents, and investments	$	137,709	$	—	$	—	$	137,709

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2018

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment consists of the following:

	At December 31,
	2018			2017
Computer equipment	$	4,208		$	3,532
Capitalized software		252			174
Website development costs		6,907			4,895
Furniture and fixtures		4,584			4,421
Leasehold improvements		10,821			10,797
Construction in progress		8,971			46
		35,743			23,865
Less accumulated depreciation		(11,474	)		(7,302	)
Property and equipment, net	$	24,269		$	16,563

Accrued Expenses, Accrued Income Taxes and Other Current Liabilities (Tables)

12 Months Ended

Dec. 31, 2018

Accrued Liabilities Current [Abstract]

Schedule of Accrued Expenses, Accrued Income Taxes and Other Current Liabilities

Accrued expenses, accrued income taxes and other current liabilities consist of the following:

	At December 31,
	2018		2017
Accrued bonuses	$	8,266	$	7,807
Other accrued expenses, accrued income taxes and other current liabilities		10,388		5,781
	$	18,654	$	13,588

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2018

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Rental Commitments under Operating Leases

Future minimum rental commitments under the Company’s operating leases at December 31, 2018 are as follows:

Year Ending December 31,	Operating Lease Commitments
2019	$	11,509
2020		11,077
2021		11,184
2022		10,878
2023 and thereafter		43,327
	$	87,975

Convertible Preferred Stock and Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2018

Equity [Abstract]

Summary of Preferred Stock

Prior to the Company’s IPO, at which time all shares of Preferred Stock were converted into shares of common stock, the Company’s Preferred Stock consisted of the following:

	Original Issue Price Per Share		Shares Authorized		Outstanding		Liquidation Amount		Carrying Value
Series A Preferred Stock	$	0.525053		3,333,000		2,824,703	$	1,483	$	1,483
Series B Preferred Stock	$	0.780899		3,329,497		2,938,486		2,295		2,295
Series C Preferred Stock	$	0.849012		1,648,978		1,550,612		1,316		1,316
Series D Preferred Stock	$	40.642989		1,673,105		1,673,105		68,000		67,872
Series E Preferred Stock	$	54.190650		1,107,202		1,107,202		60,000		59,732
				11,091,782		10,094,108	$	133,094	$	132,698

Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity

The following is a summary of the stock option activity for all stock‑based compensation plans during the year ended December 31, 2018:

	Common Stock			Weighted-Average Exercise Price for Equity		Weighted-Average Contractual Life (In Years)		Aggregate Intrinsic Value⁽¹⁾
Outstanding, December 31, 2017		5,041,540		$	1.60		6.0	$	143,059
Granted		—			—		—		—
Exercised		(3,197,179	)	1.14			—		111,227
Forfeited and cancelled		(36,846	)	5.47			—
Outstanding, December 31, 2018		1,807,515		$	2.35		5.9	$	56,716
Options exercisable at December 31, 2018		1,522,101		$	1.58	5.7		$	48,928

⁽¹⁾	The aggregate intrinsic value was calculated based on the positive difference, if any, between the estimated fair value of our common stock on December 31, 2018, 2017, and 2016 respectively, or the date of exercise, as appropriate, and the exercise price of the underlying options.

Summary of Restricted Stock Unit Activity

The following is a summary of the RSU activity during the year ended December 31, 2018:

	Number of Shares			Weighted- Average Grant Date Fair Value		Aggregate Intrinsic Value
Unvested outstanding, December 31, 2017		2,372,380		$	12.34	$	71,124
Granted		1,917,043		35.79
Vested		(1,087,279	)	14.71
Cancelled		(229,142	)	19.46
Unvested outstanding, December 31, 2018		2,973,002		$	26.06	$	100,279

Summary of Stock-based Compensation Expense by Award Type

	Year Ended December 31,
	2018		2017		2016
Options	$	247	$	281	$	322
RSUs		20,547		4,747		—
Total stock-based compensation	$	20,794	$	5,028	$	322

Summary of Allocation of Stock-based Compensation Expense

	Year Ended December 31,
	2018		2017		2016
Cost of revenue	$	354	$	151	$	18
Sales and marketing expense		5,111		1,911		163
Product, technology, and development expense		9,865		1,637		104
General and administrative expense		5,464		1,329		37
	$	20,794	$	5,028	$	322

Summary of Shares of Common Stock Reserved for Future Issuance

At December 31, 2018, the Company had reserved the following shares of voting common stock for future issuance:

Common stock options outstanding			1,807,515
Restricted stock units outstanding			2,973,002
Shares available for issuance under the 2017 Plan			6,839,584
Total shares of authorized common stock reserved for future issuance			11,620,101

Earnings Per Share (Tables)

12 Months Ended

Dec. 31, 2018

Earnings Per Share [Abstract]

Schedule of Reconciliation of Numerator and Denominator Used in Calculation of Basic and Diluted Net (Loss) Income Per Share

The following table presents a reconciliation of the numerator and denominator used in the calculation of basic and diluted net income (loss) per share:

	Year Ended December 31,
	2018		2017			2016
Numerator:
Net income	$	65,170	$	13,199		$	6,497
Deemed dividend to preferred stockholders		—		—			(32,087	)
Net income attributable to participating securities		—		(6,098	)		—
Net income (loss) attributable to common stockholders — basic	$	65,170	$	7,101		$	(25,590	)
Net income	$	65,170	$	13,199		$	6,497
Deemed dividend to preferred stockholders		—		—			(32,087	)
Net income attributable to participating securities		—		(5,829	)		—
Net income (loss) attributable to common stockholders — diluted	$	65,170	$	7,370		$	(25,590	)
Denominator:
Weighted–average number of shares of common stock used in computing net income per share attributable to common stockholders — basic		108,833,028		55,835,265			44,138,922
Dilutive effect of share equivalents resulting from stock options		3,009,748		4,290,362			—
Dilutive effect of share equivalents resulting from unvested restricted stock units		1,521,936		511,957			—
Weighted–average number of shares of common stock used in computing net income per share — diluted		113,364,712		60,637,584			44,138,922
Net income (loss) per share attributable to common stockholders:
Basic	$	0.60	$	0.13		$	(0.58	)
Diluted		0.57		0.12			(0.58	)

Schedule of Potentially Dilutive Common Stock Equivalents Excluded from Calculation of Diluted Weighted-average Shares Outstanding

	Year Ended December 31,
	2018		2017		2016
Stock options outstanding		—		—		5,698,812
Restricted stock units outstanding		126,816		829		1,580,094
Convertible preferred stock		—		—		10,094,108

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of Domestic and Foreign Components of Income Before Income Taxes

The domestic and foreign components of income before income taxes are as follows:

	Year Ended December 31,
	2018		2017		2016
United States	$	24,426	$	15,543	$	8,919
Foreign		1,058		294		26
Income before income taxes	$	25,484	$	15,837	$	8,945

Schedule of (Benefit From) Provision for Income Taxes

The (benefit from) provision for income taxes contained the following components:

	Year Ended December 31,
	2018			2017			2016
Current (benefit) provision:
Federal	$	(860	)	$	3,262		$	1,440
State		92			431			223
Foreign		122			62			3
		(646	)		3,755			1,666
Deferred (benefit) provision:
Federal		(27,675	)		(755	)		880
State		(11,499	)		(343	)		(98	)
Foreign		134			(19	)		—
		(39,040	)		(1,117	)		782
Income tax (benefit) provision	$	(39,686	)	$	2,638		$	2,448

Schedule of Effective Tax Rates Less than US Federal Statutory Rate Primarily Due to Excess Tax Deductions

	Year Ended December 31,
	2018			2017			2016
U.S. federal taxes at statutory rate		21.0	%		35.0	%		35.0	%
State taxes, net of federal benefit		(25.6	)		3.1			4.5
Nondeductible expenses		4.1			1.2			2.0
Tax deductible IPO costs		—			(9.3	)		—
Stock compensation		(127.2	)		(4.4	)		—
Foreign rate differential		(0.4	)		(0.4	)		(0.1	)
Credits		(28.4	)		(9.0	)		(15.0	)
Other		0.7			0.5			1.0
Total		(155.8	)%		16.7	%		27.4	%

Schedule of Income Tax Effect of Each Type of Temporary Difference and Carryforward

The approximate income tax effect of each type of temporary difference and carryforward as of December 31, 2018 and 2017 is as follows:

	As of December 31,
	2018			2017
Deferred tax assets:
Net operating loss carryforwards	$	34,450		$	—
Credit carryforwards		6,562			166
Stock-based compensation		1,945			1,301
Landlord allowance on leasehold improvements		1,908			1,078
Deferred rent		873			583
Accruals and reserves		1,074			606
		46,812			3,734
Deferred tax liability:
Prepaid expenses		(931	)		—
Deferred commissions		(3,187	)		—
Unbilled revenue		(227	)		—
Fixed assets		(3,581	)		(2,909	)
		(7,926	)		(2,909	)
Net deferred tax assets	$	38,886		$	825

Segment and Geographic Information (Tables)

12 Months Ended

Dec. 31, 2018

Segment Reporting [Abstract]

Summary of Operations by Segment and Geographical Area

Information regarding the Company’s operations by segment and geographical area is presented below:

	Year Ended December 31,
	2018⁽¹⁾		2017		2016
Segment revenue:
United States	$	437,166	$	307,472	$	195,824
International		16,920		9,389		2,317
Total revenue	$	454,086	$	316,861	$	198,141

	Year Ended December 31,
	2018⁽¹⁾			2017			2016
Segment income (loss) from operations:
United States	$	58,387		$	41,586		$	27,461
International		(35,196	)		(26,312	)		(18,890	)
Total income from operations	$	23,191		$	15,274		$	8,571

⁽¹⁾	Included in the year ended December 31, 2018 United States and International segments are revenue adjustments of $94 and $32, respectively, and operating income adjustments of $8,613 and $811, respectively, related to the Company's adoption of ASC 606.

Quarterly Financial Results (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Data [Abstract]

Schedule of Unaudited Quarterly Financial Information

	Fourth Quarter		Third Quarter⁽¹⁾		Second Quarter⁽¹⁾		First Quarter⁽¹⁾
Year ended December 31, 2018
Revenue	$	126,090	$	119,125	$	110,296	$	98,575
Cost of revenue		6,871		6,412		5,959		5,569
Gross profit		119,219		112,713		104,337		93,006
Income from operations		6,902		5,877		3,953		6,459
Net income		12,450		13,882		33,343		5,495
Basic net income per share⁽¹⁾	$	0.11	$	0.13	$	0.31	$	0.05
Diluted net income per share ⁽¹⁾	$	0.11	$	0.12	$	0.29	$	0.05
Year ended December 31, 2017
Revenue	$	90,597	$	82,989	$	76,240	$	67,035
Cost of revenue		5,242		4,720		4,322		3,325
Gross profit		85,355		78,269		71,918		63,710
Income from operations		32		2,863		5,995		6,384
Net income		2,267		2,379		4,346		4,207
Basic net income per share⁽¹⁾	$	0.02	$	0.02	$	0.04	$	0.04
Diluted net income per share ⁽¹⁾	$	0.02	$	0.02	$	0.04	$	0.04

⁽¹⁾	The amounts were computed independently for each quarter, and the sum of the quarters may not total the annual amounts.

⁽²⁾	The amounts for the three months ended March 31, 2018, June 30, 2018 and September 30, 2018 were adjusted from previously reported amounts as a result of the adoption of ASC 606. Refer to the tables below for a reconciliation of the previously reported amounts to the adjusted amounts.

	First Quarter
	As Reported		ASC 606 Adjustment			As Adjusted
Three Months ended March 31, 2018
Revenue	$	98,701	$	(126	)	$	98,575
Cost of revenue		5,569		—			5,569
Gross profit		93,132		(126	)		93,006
Income from operations		3,922		2,537			6,459
Net income		3,651		1,844			5,495
Basic net income per share	$	0.03	$	0.02		$	0.05
Diluted net income per share	$	0.03	$	0.02		$	0.05

	Second Quarter
	As Reported		ASC 606 Adjustment			As Adjusted
Three Months ended June 30, 2018
Revenue	$	110,325	$	(29	)	$	110,296
Cost of revenue		5,959		—			5,959
Gross profit		104,366		(29	)		104,337
Income from operations		1,444		2,509			3,953
Net income		31,265		2,078			33,343
Basic net income per share	$	0.29	$	0.02		$	0.31
Diluted net income per share	$	0.28	$	0.01		$	0.29

	Third Quarter
	As Reported		ASC 606 Adjustment		As Adjusted
Three Months ended September 30, 2018
Revenue	$	119,042	$	83	$	119,125
Cost of revenue		6,412		—		6,412
Gross profit		112,630		83		112,713
Income from operations		3,635		2,242		5,877
Net income		12,135		1,747		13,882
Basic net income per share	$	0.11	$	0.02	$	0.13
Diluted net income per share	$	0.11	$	0.01	$	0.12

Organization and Business Description - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Oct. 16, 2017	Dec. 31, 2018	Dec. 31, 2017
Organization And Business Description [Line Items]
State of incorporation		Delaware
Date of incorporation		Jun. 26, 2015
Issuance of stock, net of issuance/offering costs			$ 43,240
Net proceeds received after deducting underwriting discounts and commissions and offering costs			$ 47,690
Conversion of convertible securities into shares of common stock	9,091,484
Preferred stock, shares outstanding		0	0
Class A Common Stock
Organization And Business Description [Line Items]
Conversion of convertible securities into shares of common stock	60,564,678
Class A Common Stock \| Selling Shareholders
Organization And Business Description [Line Items]
Issuance of stock, net of issuance/offering costs, Shares	7,605,000
Class A Common Stock \| Subsequent Conversion
Organization And Business Description [Line Items]
Conversion of convertible securities into shares of common stock	40,376,452
Class B Common Stock
Organization And Business Description [Line Items]
Conversion of convertible securities into shares of common stock	40,376,452
IPO
Organization And Business Description [Line Items]
Preferred stock, shares outstanding	0
IPO \| Class A Common Stock
Organization And Business Description [Line Items]
Issuance of stock, net of issuance/offering costs, Shares	3,205,000
Number of shares issued for services	705,000
Offering price per share	$ 16.00
Issuance of stock, net of issuance/offering costs	$ 51,300
Net proceeds received after deducting underwriting discounts and commissions and offering costs	43,200
Underwriting discounts and commissions	3,600
Stock issuance costs	$ 4,500
Conversion of convertible securities into shares of common stock	20,188,226
IPO \| Convertible Preferred Stock
Organization And Business Description [Line Items]
Preferred stock, shares outstanding	0

Summary of Significant Accounting Policies - Additional Information (Details)

3 Months Ended

12 Months Ended

Dec. 31, 2018

USD ($)

$ / shares

Sep. 30, 2018

USD ($)

$ / shares

Jun. 30, 2018

USD ($)

$ / shares

Mar. 31, 2018

USD ($)

$ / shares

Dec. 31, 2017

USD ($)

$ / shares

Sep. 30, 2017

USD ($)

$ / shares

Jun. 30, 2017

USD ($)

$ / shares

Mar. 31, 2017

USD ($)

$ / shares

Dec. 31, 2018

USD ($)

Customer

$ / shares

Dec. 31, 2017

USD ($)

Customer

$ / shares

Dec. 31, 2016

USD ($)

Customer

$ / shares

Jan. 01, 2018

USD ($)

Oct. 11, 2017

USD ($)

Summary Of Significant Accounting Policies [Line Items]

Payment of revenue, performance obligation, description of payment terms

thirty to sixty

Accounts receivable, net

$ 13,614,000

$ 12,577,000

$ 13,614,000

$ 12,577,000

268,290,000

176,594,000

268,290,000

176,594,000

Liabilities

74,179,000

49,569,000

74,179,000

49,569,000

$ 126,090,000

$ 119,125,000

$ 110,296,000

$ 98,575,000

$ 90,597,000

$ 82,989,000

$ 76,240,000

$ 67,035,000

454,086,000

^[1]

316,861,000

$ 198,141,000

315,939,000

236,165,000

154,125,000

25,484,000

15,837,000

8,945,000

Basic net income per share | $ / shares

$ (39,686,000)

$ 2,638,000

$ 2,448,000

$ 0.11

$ 0.13

$ 0.31

$ 0.05

$ 0.02

$ 0.04

$ 0.60

$ 0.13

$ (0.58)

Diluted net income per share | $ / shares

$ 0.11

$ 0.12

$ 0.29

$ 0.05

$ 0.02

$ 0.04

$ 0.57

$ 0.12

$ (0.58)

Costs to obtain a contract

$ 12,505,000

$ 3,207,000

Amortization expense recognized related to costs to obtain a contract

$ 3,689,000

Amount of transaction price allocated to performance obligations

false

Description of significant off-balance sheet risk

The Company has no significant offbalance sheet risk, such as foreign exchange contracts, option contracts, or other foreign hedging arrangements.

Amortization (accretion) of premiums or discounts

$ 0

Realized gains or losses on investments

$ 0

Other than temporary impairments recognized in statements of operations

Restricted cash

2,671,000

$ 1,843,000

2,671,000

1,843,000

Impairment of long lived assets

$ 0

Liabilities for uncertain tax positions

$ 0

Unrecognized stock-based compensation expense related to stock-based awards

$ 2,500,000

Expected dividend yield

0.00%

Estimated forfeiture rate

5.00%

Weighted average fair value of options granted | $ / shares

$ 0.90

Options granted during period | shares

Advertising expense

$ 238,640,000

$ 173,186,000

$ 112,167,000

Website and Software Development Costs

Summary Of Significant Accounting Policies [Line Items]

Estimated useful life

3 years

Software and website development costs capitalized

2,012,000

2,215,000

$ 2,012,000

2,215,000

Amortization expense

$ 1,508,000

$ 812,000

$ 343,000

Maximum

Summary Of Significant Accounting Policies [Line Items]

Maturity of certificates of deposit, description

As of December 31, 2018 and 2017, investments consisted of U.S. certificates of deposit (“CDs”) with remaining maturities of less than twelve months.

Maturity period of certificates of deposit

12 months

Sales Revenue, Net | Concentration of Credit Risk

Summary Of Significant Accounting Policies [Line Items]

Concentration of credit risk, percentage

10.00%

Number of major customers | Customer

Net Accounts Receivable | Advertising Customers

Summary Of Significant Accounting Policies [Line Items]

Unbilled accounts receivables

5,815,000

$ 1,845,000

$ 5,815,000

$ 1,845,000

Net Accounts Receivable | Concentration of Credit Risk

Summary Of Significant Accounting Policies [Line Items]

Number of major customers | Customer

Net Accounts Receivable | Concentration of Credit Risk | Customer One

Summary Of Significant Accounting Policies [Line Items]

Concentration of credit risk, percentage

21.00%

29.00%

Net Accounts Receivable | Concentration of Credit Risk | Customer Two

Summary Of Significant Accounting Policies [Line Items]

Concentration of credit risk, percentage

14.00%

17.00%

Marketplace Subscription Revenue

Summary Of Significant Accounting Policies [Line Items]

Summary Of Significant Accounting Policies [Line Items]

$ 405,780,000

ASC 606

Accounts receivable, net

13,390,000

Summary Of Significant Accounting Policies [Line Items]

179,789,000

Liabilities

49,722,000

ASC 606 | Adjustments

Reduction to deferred tax assets

978,000

10,030,000

Liabilities

$ 83,000

$ (29,000)

$ (126,000)

126,000

(9,298,000)

9,424,000

Basic net income per share | $ / shares

$ 2,436,000

$ 0.02

$ 0.07

Diluted net income per share | $ / shares

$ 0.01

$ 0.02

$ 0.06

ASC 606 | Marketplace Subscription Revenue | Adjustments

Summary Of Significant Accounting Policies [Line Items]

Accounts receivable, net

939,000

$ 939,000

813,000

$ 712,000

712,000

$ 623,000

126,000

126,000

Accounting Standards Update 2016-09

37,000

Summary Of Significant Accounting Policies [Line Items]

Revenue by Revenue Stream [Abstract]

$ (40,765,000)

$ (681,000)

[1]	Included in the year ended December 31, 2018 United States and International segments are revenue adjustments of $94 and $32, respectively, and operating income adjustments of $8,613 and $811, respectively, related to the Company's adoption of ASC 606.

Summary of Significant Accounting Policies - Summary of Revenue from Contracts With Customers by Revenue (Details) - USD ($)
$ in Thousands

3 Months Ended

12 Months Ended

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2017

Sep. 30, 2017

Jun. 30, 2017

Mar. 31, 2017

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

Marketplace Subscription Revenue

$ 126,090

$ 119,125

$ 110,296

$ 98,575

$ 90,597

$ 82,989

$ 76,240

$ 67,035

$ 454,086

^[1]

$ 316,861

$ 198,141

Revenue by Revenue Stream [Abstract]

Advertising and Other Revenue

405,780

Revenue by Revenue Stream [Abstract]

Summary Of Significant Accounting Policies [Line Items]

$ 48,306

[1]	Included in the year ended December 31, 2018 United States and International segments are revenue adjustments of $94 and $32, respectively, and operating income adjustments of $8,613 and $811, respectively, related to the Company's adoption of ASC 606.

Summary of Significant Accounting Policies - Summary of Adjustments in Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 34,887		$ 87,709
Investments	122,800		50,000
Accounts receivable, net	13,614		12,577
Prepaid expenses and prepaid income taxes	10,144		5,313
Deferred contract costs	5,253
Other current assets	7,410		1,605
Restricted cash	750
Total current assets	194,858		157,204
Property and equipment, net	24,269		16,563
Restricted cash	1,921		1,843
Deferred tax assets	38,886		825
Deferred contract costs, net of current portion	7,252
Other long–term assets	1,104		159
Total assets	268,290		176,594
Current liabilities:
Accounts payable	34,345		23,908
Accrued expenses, accrued income taxes and other current liabilities	18,654		13,588
Deferred revenue	8,811		4,305
Deferred rent	1,693		1,165
Total current liabilities	63,503		42,966
Deferred rent, net of current portion	9,395		5,648
Other non–current liabilities	1,281		955
Total liabilities	74,179		49,569
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock
Additional paid–in capital	184,216		185,190
Retained earnings (accumulated deficit)	9,713		(58,499)
Accumulated other comprehensive income	71		228
Total stockholders’ equity	194,111		127,025	$ (67,972)	$ (16,131)
Total liabilities and stockholders’ equity	268,290		176,594
ASC 606
Current assets:
Cash and cash equivalents		$ 87,709
Investments		50,000
Accounts receivable, net		13,390
Prepaid expenses and prepaid income taxes		5,313
Deferred contract costs		1,424
Other current assets		1,605
Total current assets		159,441
Property and equipment, net		16,563
Restricted cash		1,843
Deferred contract costs, net of current portion		1,783
Other long–term assets		159
Total assets		179,789
Current liabilities:
Accounts payable		23,908
Accrued expenses, accrued income taxes and other current liabilities		13,588
Deferred revenue		4,305
Deferred tax liabilities		153
Deferred rent		1,165
Total current liabilities		43,119
Deferred rent, net of current portion		5,648
Other non–current liabilities		955
Total liabilities		49,722
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock
Additional paid–in capital		185,190
Retained earnings (accumulated deficit)		(55,457)
Accumulated other comprehensive income		228
Total stockholders’ equity		130,067
Total liabilities and stockholders’ equity		179,789
Adjustments \| ASC 606
Current assets:
Total assets	10,030
Current liabilities:
Total liabilities	0
Adjustments \| ASC 606 \| Marketplace Subscription Revenue
Current assets:
Accounts receivable, net	939	813
Total current assets	939	813
Deferred tax assets	(227)	(190)
Total assets	712	623
Current liabilities:
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock
Retained earnings (accumulated deficit)	712	623
Total stockholders’ equity	712	623
Total liabilities and stockholders’ equity	712	623
Adjustments \| ASC 606 \| Costs To Obtain a Contract
Current assets:
Deferred contract costs	5,253	1,424
Total current assets	5,253	1,424
Deferred tax assets	(3,187)	(635)
Deferred contract costs, net of current portion	7,252	1,783
Total assets	9,318	2,572
Current liabilities:
Deferred tax liabilities		153
Total current liabilities		153
Total liabilities		153
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock
Retained earnings (accumulated deficit)	9,318	2,419
Total stockholders’ equity	9,318	2,419
Total liabilities and stockholders’ equity	9,318	2,572
Class A Common Stock
Stockholders’ equity:
Common stock	90		78
Class A Common Stock \| ASC 606
Stockholders’ equity:
Common stock		78
Class B Common Stock
Stockholders’ equity:
Common stock	$ 21		$ 28
Class B Common Stock \| ASC 606
Stockholders’ equity:
Common stock		$ 28

Summary of Significant Accounting Policies - Summary of Compare the Reported Consolidated Balance Sheet to Pro-forma Amounts had Previous Guidance Been in Effect (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 34,887		$ 87,709
Investments	122,800		50,000
Accounts receivable, net	13,614		12,577
Prepaid income taxes and prepaid income taxes	10,144		5,313
Deferred contract costs	5,253
Other current assets	7,410		1,605
Restricted cash	750
Total current assets	194,858		157,204
Property and equipment, net	24,269		16,563
Restricted cash	1,921		1,843
Deferred tax assets	38,886		825
Deferred contract costs, net of current portion	7,252
Other long–term assets	1,104		159
Total assets	268,290		176,594
Current liabilities:
Accounts payable	34,345		23,908
Accrued expenses, accrued income taxes and other current liabilities	18,654		13,588
Deferred revenue	8,811		4,305
Deferred rent	1,693		1,165
Total current liabilities	63,503		42,966
Deferred rent, net of current portion	9,395		5,648
Other non–current liabilities	1,281		955
Total liabilities	74,179		49,569
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock
Additional paid–in capital	184,216		185,190
Retained earnings (accumulated deficit)	9,713		(58,499)
Accumulated other comprehensive income	71		228
Total stockholders’ equity	194,111		127,025	$ (67,972)	$ (16,131)
Total liabilities and stockholders’ equity	268,290		176,594
ASC 606
Current assets:
Cash and cash equivalents		$ 87,709
Investments		50,000
Accounts receivable, net		13,390
Prepaid income taxes and prepaid income taxes		5,313
Deferred contract costs		1,424
Other current assets		1,605
Total current assets		159,441
Property and equipment, net		16,563
Restricted cash		1,843
Deferred contract costs, net of current portion		1,783
Other long–term assets		159
Total assets		179,789
Current liabilities:
Accounts payable		23,908
Accrued expenses, accrued income taxes and other current liabilities		13,588
Deferred revenue		4,305
Deferred rent		1,165
Total current liabilities		43,119
Deferred rent, net of current portion		5,648
Other non–current liabilities		955
Total liabilities		49,722
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock
Additional paid–in capital		185,190
Retained earnings (accumulated deficit)		(55,457)
Accumulated other comprehensive income		228
Total stockholders’ equity		130,067
Total liabilities and stockholders’ equity		179,789
Adjustments \| ASC 606
Current assets:
Total assets	10,030
Current liabilities:
Total liabilities	0
Adjustments \| ASC 606 \| Marketplace Subscription Revenue
Current assets:
Accounts receivable, net	939	813
Total current assets	939	813
Deferred tax assets	(227)	(190)
Total assets	712	623
Current liabilities:
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock
Retained earnings (accumulated deficit)	712	623
Total stockholders’ equity	712	623
Total liabilities and stockholders’ equity	712	623
Adjustments \| ASC 606 \| Costs To Obtain a Contract
Current assets:
Deferred contract costs	5,253	1,424
Total current assets	5,253	1,424
Deferred tax assets	(3,187)	(635)
Deferred contract costs, net of current portion	7,252	1,783
Total assets	9,318	2,572
Current liabilities:
Total current liabilities		153
Total liabilities		153
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock
Retained earnings (accumulated deficit)	9,318	2,419
Total stockholders’ equity	9,318	2,419
Total liabilities and stockholders’ equity	9,318	2,572
Pro Forma as if the Previous Accounting Guidance was in Effect \| ASC 606
Current assets:
Cash and cash equivalents	34,887
Investments	122,800
Accounts receivable, net	12,675
Prepaid income taxes and prepaid income taxes	10,144
Other current assets	7,410
Restricted cash	750
Total current assets	188,666
Property and equipment, net	24,269
Restricted cash	1,921
Deferred tax assets	42,300
Other long–term assets	1,104
Total assets	258,260
Current liabilities:
Accounts payable	34,345
Accrued expenses, accrued income taxes and other current liabilities	18,654
Deferred revenue	8,811
Deferred rent	1,693
Total current liabilities	63,503
Deferred rent, net of current portion	9,395
Other non–current liabilities	1,281
Total liabilities	74,179
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock
Additional paid–in capital	184,216
Retained earnings (accumulated deficit)	(317)
Accumulated other comprehensive income	71
Total stockholders’ equity	184,081
Total liabilities and stockholders’ equity	258,260
Class A Common Stock
Stockholders’ equity:
Common stock	90		78
Class A Common Stock \| ASC 606
Stockholders’ equity:
Common stock		78
Class A Common Stock \| Pro Forma as if the Previous Accounting Guidance was in Effect \| ASC 606
Stockholders’ equity:
Common stock	90
Class B Common Stock
Stockholders’ equity:
Common stock	21		$ 28
Class B Common Stock \| ASC 606
Stockholders’ equity:
Common stock		$ 28
Class B Common Stock \| Pro Forma as if the Previous Accounting Guidance was in Effect \| ASC 606
Stockholders’ equity:
Common stock	$ 21

Summary of Significant Accounting Policies - Summary of Changes on Consolidated Statement of Operations as a Result of Adoption of ASC 606 (Details) - USD ($)
$ / shares in Units, $ in Thousands

3 Months Ended

12 Months Ended

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2017

Sep. 30, 2017

Jun. 30, 2017

Mar. 31, 2017

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

$ 126,090

$ 119,125

$ 110,296

$ 98,575

$ 90,597

$ 82,989

$ 76,240

$ 67,035

$ 454,086

^[1]

$ 316,861

$ 198,141

6,871

6,412

5,959

5,569

5,242

4,720

4,322

3,325

24,811

^[2]

17,609

^[2]

9,575

^[2]

119,219

112,713

104,337

93,006

85,355

78,269

71,918

63,710

429,275

299,252

188,566

Product, technology, and development

315,939

236,165

154,125

47,866

22,470

11,453

General and administrative

39,475

22,688

12,783

Depreciation and amortization

2,804

2,655

1,634

406,084

283,978

179,995

6,902

5,877

3,953

6,459

2,863

5,995

6,384

23,191

^[1]

15,274

8,571

Interest income

2,283

869

416

Other income (expense)

(306)

(42)

Total other income, net

2,293

563

374

25,484

15,837

8,945

(39,686)

2,638

2,448

$ 12,450

$ 13,882

$ 33,343

$ 5,495

$ 2,267

$ 2,379

$ 4,346

$ 4,207

$ 65,170

$ 13,199

$ 6,497

$ 0.11

$ 0.13

$ 0.31

$ 0.05

$ 0.02

$ 0.04

$ 0.60

$ 0.13

$ (0.58)

Marketplace Subscription Revenue

$ 0.11

$ 0.12

$ 0.29

$ 0.05

$ 0.02

$ 0.04

$ 0.57

$ 0.12

$ (0.58)

Summary Of Significant Accounting Policies [Line Items]

Summary Of Significant Accounting Policies [Line Items]

$ 405,780

Adjustments | ASC 606

$ 83

$ (29)

$ (126)

126

(29)

(126)

(9,298)

2,242

2,509

2,537

9,424

$ 2,436

$ 1,747

$ 2,078

$ 1,844

$ 0.02

$ 0.07

Adjustments | ASC 606 | Costs To Obtain a Contract

$ 0.01

$ 0.02

$ 0.06

$ (9,298)

(9,298)

9,298

9,298

2,399

$ 6,899

$ 0.07

Adjustments | ASC 606 | Marketplace Subscription Revenue

$ 0.06

Summary Of Significant Accounting Policies [Line Items]

$ 126

126

126

126

Pro Forma as if the Previous Accounting Guidance was in Effect | ASC 606

Summary Of Significant Accounting Policies [Line Items]

$ 119,042

$ 110,325

$ 98,701

453,960

6,412

5,959

5,569

24,811

112,630

104,366

93,132

429,149

Product, technology, and development

325,237

47,866

General and administrative

39,475

Depreciation and amortization

2,804

415,382

3,635

1,444

3,922

13,767

Interest income

2,283

Other income (expense)

Total other income, net

2,293

16,060

(42,122)

$ 12,135

$ 31,265

$ 3,651

$ 58,182

$ 0.11

$ 0.29

$ 0.03

$ 0.53

$ 0.11

$ 0.28

$ 0.03

$ 0.51

[1]	Included in the year ended December 31, 2018 United States and International segments are revenue adjustments of $94 and $32, respectively, and operating income adjustments of $8,613 and $811, respectively, related to the Company's adoption of ASC 606.
[2]	Includes depreciation and amortization expense for the years ended December 31, 2018, 2017, and 2016 of $2,225 $1,140, and $438, respectively.

Summary of Significant Accounting Policies - Summary of Changes on Consolidated Statement of Cash Flows as a Result of Adoption of ASC 606 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Activities
Net income	$ 65,170	$ 13,199	$ 6,497
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	5,029	3,795	2,072
Unrealized currency (gain) loss on foreign denominated transactions	(190)	128
Deferred taxes	(39,040)	(1,117)	782
Provision for doubtful accounts	1,680	1,117	508
Stock–based compensation expense	20,794	5,028	322
Amortization of deferred contract costs	3,689
Changes in operating assets and liabilities:
Accounts receivable, net	(1,911)	(7,039)	(1,432)
Prepaid expenses, prepaid income taxes, and other assets	(11,753)	(2,287)	(2,226)
Deferred contracts costs	(12,987)
Accounts payable	9,345	6,244	5,811
Accrued expenses, accrued income taxes and other current liabilities	2,695	5,191	4,118
Deferred revenue	4,508	962	1,856
Deferred rent	4,289	227	1,927
Other non–current liabilities	405	243	590
Net cash provided by operating activities	51,723	$ 25,691	$ 20,004
Adjustments \| ASC 606 \| Costs To Obtain a Contract
Operating Activities
Net income	6,899
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred taxes	2,399
Amortization of deferred contract costs	3,689
Changes in operating assets and liabilities:
Deferred contracts costs	(12,987)
Adjustments \| ASC 606 \| Marketplace Subscription Revenue
Operating Activities
Net income	89
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred taxes	37
Changes in operating assets and liabilities:
Accounts receivable, net	(126)
Pro Forma as if the Previous Accounting Guidance was in Effect \| ASC 606
Operating Activities
Net income	58,182
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	5,029
Unrealized currency (gain) loss on foreign denominated transactions	(190)
Deferred taxes	(41,476)
Provision for doubtful accounts	1,680
Stock–based compensation expense	20,794
Changes in operating assets and liabilities:
Accounts receivable, net	(1,785)
Prepaid expenses, prepaid income taxes, and other assets	(11,753)
Accounts payable	9,345
Accrued expenses, accrued income taxes and other current liabilities	2,695
Deferred revenue	4,508
Deferred rent	4,289
Other non–current liabilities	405
Net cash provided by operating activities	$ 51,723

Summary of Significant Accounting Policies - Summary of Opening and Closing Balances of Receivables and Contract Assets From Contracts with Customers (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Capitalized Contract Cost [Line Items]
Accounts Receivable, net	$ 13,614		$ 12,577
Contract Assets (current)	5,253
Contract Assets (non-current)	$ 7,252
ASC 606
Capitalized Contract Cost [Line Items]
Accounts Receivable, net		$ 13,390
Contract Assets (current)		1,424
Contract Assets (non-current)		$ 1,783

Summary of Significant Accounting Policies - Summary of Changes in Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Receivables [Abstract]
Balance at Beginning of Period	$ 494	$ 164	$ 75
Provision for doubtful accounts	1,680	1,117	508
Write–offs, net of recoveries	(1,695)	(787)	(419)
Balance at End of Period	$ 479	$ 494	$ 164

Summary of Significant Accounting Policies - Schedule of Estimated Useful Lives of Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2018
Computer Equipment
Property Plant And Equipment [Line Items]
Estimated Useful Life	3 years
Capitalized Software
Property Plant And Equipment [Line Items]
Estimated Useful Life	3 years
Website Development Costs
Property Plant And Equipment [Line Items]
Estimated Useful Life	3 years
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Estimated Useful Life	5 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Estimated Useful Life	Lesser of asset life or lease term

Summary of Significant Accounting Policies - Schedule of Weighted-Average Assumptions Utilized to Determine Fair Value of Options Granted (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected dividend yield	0.00%
Expected volatility		49.00%
Risk–free interest rate		1.57%
Expected term (in years)		6 years 26 days

Fair Value of Financial Instruments Including Cash, Cash Equivalents and Investments - Schedule of Fair Value Levels, Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:	$ 34,887	$ 87,709
Investments:	122,800	50,000
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments:	$ 122,800	$ 50,000
Debt Securities, Held-to-maturity, Type [Extensible List]	us-gaap:CertificatesOfDepositMember	us-gaap:CertificatesOfDepositMember
Total	$ 122,824	$ 110,709
Fair Value, Measurements, Recurring \| Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:	24	60,709
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1 Inputs)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	24	60,709
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1 Inputs) \| Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:	24	60,709
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2 Inputs)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments:	$ 122,800	$ 50,000
Debt Securities, Held-to-maturity, Type [Extensible List]	us-gaap:CertificatesOfDepositMember	us-gaap:CertificatesOfDepositMember
Total	$ 122,800	$ 50,000

Fair Value of Financial Instruments Including Cash, Cash Equivalents and Investments - Schedule of Cash, Cash Equivalents, and Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Cash and cash equivalents due in 90 days or less, Amortized Cost	$ 34,887	$ 87,709
Certificates of deposit due in one year or less, Amortized Cost	122,800	50,000
Total cash, cash equivalents, and investments, Amortized Cost	157,687	137,709
Cash and cash equivalents due in 90 days or less, Estimated Fair Value	34,887	87,709
Certificates of deposit due in one year or less, Estimated Fair Value	122,800	50,000
Total cash, cash equivalents, and investments, Estimated Fair Value	$ 157,687	$ 137,709

Property and Equipment, Net - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 35,743	$ 23,865
Less accumulated depreciation	(11,474)	(7,302)
Property and equipment, net	24,269	16,563
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,208	3,532
Capitalized Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	252	174
Website Development Costs
Property Plant And Equipment [Line Items]
Property and equipment, gross	6,907	4,895
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,584	4,421
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	10,821	10,797
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 8,971	$ 46

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Depreciation and amortization	$ 5,029	$ 3,795	$ 2,072
Capitalized Website and Software Development Costs
Property Plant And Equipment [Line Items]
Depreciation and amortization	5,029	$ 3,795	$ 2,072
Construction in Progress
Property Plant And Equipment [Line Items]
Increase in property and equipment	$ 8,925

Accrued Expenses, Accrued Income Taxes and Other Current Liabilities - Schedule of Accrued Expenses, Accrued Income Taxes and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Liabilities Current [Abstract]
Accrued bonuses	$ 8,266	$ 7,807
Other accrued expenses, accrued income taxes and other current liabilities	10,388	5,781
Accrued expenses, accrued income taxes and other current liabilities, Total	$ 18,654	$ 13,588

Commitments and Contingencies - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 19, 2018 ft²	Mar. 11, 2016 ft²	Oct. 08, 2014 ft²
Commitments And Contingencies [Line Items]
Deferred rent and rent incentives	$ 11,088	$ 6,813
Deferred rent and rent incentives, current	1,693	1,165
Deferred rent and rent incentives, noncurrent	9,395	5,648
Rent expense	$ 7,711	$ 5,994	$ 3,678
Cambridge, Massachusetts \| 121 First St
Commitments And Contingencies [Line Items]
Square feet of rentable office space \| ft²				48,393
Operating lease, option to extend	option to extend the lease term for two additional periods of five years each
Cambridge, Massachusetts \| 55 Cambridge Parkway
Commitments And Contingencies [Line Items]
Square feet of rentable office space \| ft²					51,923
Operating lease, option to extend	option to extend the lease term for one additional period of five years
Cambridge, Massachusetts \| 2 Canal Park
Commitments And Contingencies [Line Items]
Square feet of rentable office space \| ft²						48,059
Operating lease, option to extend	option to extend the lease term for one additional period of five years

Commitments and Contingencies - Schedule of Future Minimum Rental Commitments under Operating Leases (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2019	$ 11,509
2020	11,077
2021	11,184
2022	10,878
2023 and thereafter	43,327
Total	$ 87,975

Convertible Preferred Stock and Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands				12 Months Ended
	Oct. 16, 2017	Jun. 21, 2017	Aug. 23, 2016	Dec. 31, 2018	Dec. 31, 2016	Dec. 31, 2017	Oct. 11, 2017
Class Of Stock [Line Items]
Deemed dividend to preferred stockholders					$ 32,087
Preferred stock, shares authorized	10,000,000	11,091,782					11,091,782
Preferred stock, par value	$ 0.001	$ 0.001
Common stock exercise feature				the number of shares of common stock as to which each outstanding option to purchase common stock was exercisable for and each outstanding RSU was convertible into was adjusted such that upon exercise of outstanding stock options or vesting of outstanding RSUs, each holder would receive two fully paid and nonassessable shares of Class A common stock and four fully paid and nonassessable shares of Class B common stock in respect of each share of common stock previously underlying such option or RSU
Percentage of common stock exercise price adjusted		0.167%
Percentage of common stock fair value adjusted prior to recapitalization		0.167%
Conversion of convertible securities into shares of common stock	9,091,484
Preferred stock, shares outstanding				0		0
IPO
Class Of Stock [Line Items]
Preferred stock, shares outstanding	0
Series E Preferred Stock
Class Of Stock [Line Items]
Offering amount, net of issuance costs			$ 59,732
Stock issuance costs			268		$ 280
Deemed dividend to preferred stockholders			$ 32,087
Preferred stock, shares authorized		1,107,202					1,107,202
Class A Common Stock
Class Of Stock [Line Items]
Common stock, shares authorized	500,000,000	120,020,700		500,000,000		500,000,000
Common stock, par value	$ 0.001	$ 0.001		$ 0.001		$ 0.001
Common stock conversion terms				each share of Class A common stock issued and outstanding was recapitalized, reclassified, and reconstituted into two fully paid and nonassessable shares of outstanding Class A common stock and four fully paid and nonassessable shares of outstanding Class B common stock
Number of shares issued upon exercise of outstanding stock options or vesting of outstanding RSUs		2
Conversion of convertible securities into shares of common stock	60,564,678
Class A Common Stock \| IPO
Class Of Stock [Line Items]
Stock issuance costs	$ 4,500
Conversion of convertible securities into shares of common stock	20,188,226
Class A Common Stock \| Class A Common Stock Recapitalized, Reclassified And Reconstituted [Member]
Class Of Stock [Line Items]
Common stock issued in conversion		2
Class A Common Stock \| Class B Common Stock Recapitalized, Reclassified And Reconstituted [Member]
Class Of Stock [Line Items]
Common stock issued in conversion		2
Class A Common Stock \| Subsequent Conversion
Class Of Stock [Line Items]
Conversion of convertible securities into shares of common stock	40,376,452
Class B Common Stock
Class Of Stock [Line Items]
Common stock, shares authorized	100,000,000	80,013,800		100,000,000		100,000,000
Common stock, par value	$ 0.001	$ 0.001		$ 0.001		$ 0.001
Common stock conversion terms				each share of Class B common stock of the Company issued and outstanding was recapitalized, reclassified, and reconstituted into two fully paid and nonassessable shares of outstanding Class A common stock and four fully paid and nonassessable shares of outstanding Class B common stock
Number of shares issued upon exercise of outstanding stock options or vesting of outstanding RSUs		4
Conversion of convertible securities into shares of common stock	40,376,452
Class B Common Stock \| Class A Common Stock Recapitalized, Reclassified And Reconstituted [Member]
Class Of Stock [Line Items]
Common stock issued in conversion		4
Class B Common Stock \| Class B Common Stock Recapitalized, Reclassified And Reconstituted [Member]
Class Of Stock [Line Items]
Common stock issued in conversion		4
Series A Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares authorized		3,333,000					3,333,000
Series B Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares authorized		3,329,497					3,329,497
Series C Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares authorized		1,648,978					1,648,978
Series D Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares authorized		1,673,105					1,673,105

Convertible Preferred Stock and Stockholders' Equity - Common Stock - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018 Vote shares
Class Of Stock [Line Items]
Common stock conversion feature	each share of Class B common stock was convertible into one share of Class A common stock at the option of the holder at any time.
Class A Common Stock
Class Of Stock [Line Items]
Number of votes entitled to stockholders per share \| Vote	1
Conversion of stock \| shares	7,534,710
Class B Common Stock
Class Of Stock [Line Items]
Number of votes entitled to stockholders per share \| Vote	10
Class of share converted to another class	one share of Class A common stock
Conversion of stock \| shares	1

Convertible Preferred Stock and Stockholders' Equity - Summary of Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	Oct. 16, 2017	Oct. 11, 2017	Jun. 21, 2017	Dec. 31, 2016	Dec. 31, 2015
Temporary Equity [Line Items]
Shares Authorized	10,000,000	11,091,782	11,091,782
Outstanding		10,094,108
Liquidation Amount		$ 133,094
Carrying Value		$ 132,698
Series A Preferred Stock
Temporary Equity [Line Items]
Original Issue Price Per Share		$ 0.525053
Shares Authorized		3,333,000	3,333,000
Outstanding		2,824,703		2,824,703	3,049,606
Liquidation Amount		$ 1,483
Carrying Value		$ 1,483		$ 1,483	$ 1,601
Series B Preferred Stock
Temporary Equity [Line Items]
Original Issue Price Per Share		$ 0.780899
Shares Authorized		3,329,497	3,329,497
Outstanding		2,938,486		2,938,486	3,296,054
Liquidation Amount		$ 2,295
Carrying Value		$ 2,295		$ 2,295	$ 2,574
Series C Preferred Stock
Temporary Equity [Line Items]
Original Issue Price Per Share		$ 0.849012
Shares Authorized		1,648,978	1,648,978
Outstanding		1,550,612		1,550,612	1,567,855
Liquidation Amount		$ 1,316
Carrying Value		$ 1,316		$ 1,316	$ 1,331
Series D Preferred Stock
Temporary Equity [Line Items]
Original Issue Price Per Share		$ 40.642989
Shares Authorized		1,673,105	1,673,105
Outstanding		1,673,105		1,673,105	1,673,105
Liquidation Amount		$ 68,000
Carrying Value		$ 67,872		$ 67,872	$ 67,872
Series E Preferred Stock
Temporary Equity [Line Items]
Original Issue Price Per Share		$ 54.190650
Shares Authorized		1,107,202	1,107,202
Outstanding		1,107,202		1,107,202
Liquidation Amount		$ 60,000
Carrying Value		$ 59,732		$ 59,732

Stock-based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands				12 Months Ended
	Aug. 22, 2016	Aug. 15, 2015	Jun. 26, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 16, 2017	Oct. 11, 2017	Jun. 21, 2017	Dec. 31, 2006
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of options granted in period				0	0
Weighted average fair value of options granted						$ 0.90
Total stock-based compensation expense				$ 20,794	$ 5,028	$ 322
Capitalized software development costs excluded from stock-based compensation expense				490	176
Income tax benefit from stock-based compensation expense				$ 1,945	$ 1,301	$ 67
Unrecognized stock-based compensation expense related to stock-based awards								$ 2,500
Stock Options
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of options granted in period				0	0
Weighted average fair value of options granted						$ 0.90
Aggregate intrinsic value for options exercised				$ 111,227	$ 2,238	$ 2,021
Total stock-based compensation expense				247	$ 281	$ 322
Unrecognized stock-based compensation expense related to stock options				$ 186
Unrecognized stock-based compensation expense, expected period for recognition				1 year 1 month 6 days
RSUs
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of RSUs granted in period				1,917,043
Weighted average grant date fair value of RSUs granted				$ 35.79	$ 16.99	$ 3.89
Number of RSUs vested and settled during period				1,781,201
Number of RSUs vested in period				1,087,279	693,922	0
Total fair value of RSUs vested				$ 15,994	$ 2,505
Total stock-based compensation expense				$ 20,547	$ 4,747
Unrecognized stock-based compensation expense, expected period for recognition				3 years 2 months 12 days
Unrecognized stock-based compensation expense related to stock-based awards				$ 69,998
2006 Plan
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock options, granted			0
Number of RSUs granted in period			0
2006 Plan \| Class B Common Stock
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of shares authorized for issuance										3,444,668
2015 Plan
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of shares authorized for issuance			603,436
Term of authorized shares		10 years
Award expiration date	Aug. 21, 2026
Equity Incentive Plan, plan modification, description and terms				(1) the number of shares of Class A common stock was increased, on a share for share basis, by the number of shares of Class B common stock that were (a) subject to outstanding options granted under the 2006 Plan that expired, terminated, or were cancelled for any reason without having been exercised, (b) surrendered in payment of the exercise price of outstanding options granted under the 2006 Plan or (c) withheld in satisfaction of tax withholding upon exercise of outstanding options granted under the 2006 Plan, and the number of shares of Class B common stock reserved under the amended and restated 2015 Plan was decreased, on a corresponding share for share basis, (2) no new awards of Class B common stock could be granted under the amended and restated 2015 Plan, and (3) except with respect to outstanding options granted under the 2006 Plan that were exercised on or after the date of the amendment and restatement, no Class B common stock could be issued under the 2015 Plan.
2015 Plan \| Class B Common Stock
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of shares authorized for issuance									5,161,644
Number of additional shares authorized	802,562
2015 Plan \| Class B Common Stock \| Stock Options
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of shares called by each instrument									4
2015 Plan \| Class B Common Stock \| RSUs
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of shares called by each instrument									4
2015 Plan \| Class A Common Stock
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of shares authorized for issuance									3,181,740
Number of additional shares authorized	618,691
2015 Plan \| Class A Common Stock \| Stock Options
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of shares called by each instrument									2
2015 Plan \| Class A Common Stock \| RSUs
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of shares called by each instrument									2
2017 Plan
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of additional shares authorized				6,000,000
Equity incentive plan, issuance of additional shares, description and terms				Unless determined otherwise by the Compensation Committee of the Board, as of the first trading day of January of each calendar year during the term of the 2017 Plan (excluding any extensions), eligible beginning with calendar year 2019, an additional number of shares of Class A common stock will be added to the number of shares of the Company’s Class A common stock authorized to be issued or transferred under the 2017 Plan and the number of shares authorized to be issued or transferred pursuant to incentive stock options, equal to 4% of the total number of shares of our Class A common stock outstanding on the last trading day in December of the immediately preceding calendar year, or 6,000,000 shares, whichever is less, or such lesser amount as determined by the Board (the “Evergreen Increase”). The Compensation Committee of the Board determined to not effectuate the Evergreen Increase that was otherwise scheduled to have occurred on January 2, 2019.
2017 Plan \| Class A Common Stock
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Equity incentive plan, additional shares authorized percentage				4.00%
Number of shares available for issuance during period				6,839,584
2017 Plan \| Class A Common Stock \| Maximum
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of shares authorized for issuance							12,300,000
2017 Plan \| Class A Common Stock \| Awarded Under 2017 Plan
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of shares authorized for issuance							7,800,000
2017 Plan \| Class A Common Stock \| Awarded Under 2015 Plan
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of shares authorized for issuance							4,500,000

Stock-based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Common Stock
Options granted during period	0	0
Stock Options
Common Stock
Outstanding, Beginning balance	5,041,540
Options granted during period	0	0
Exercised	(3,197,179)
Forfeited and cancelled	(36,846)
Outstanding, Ending balance	1,807,515	5,041,540
Options exercisable	1,522,101
Weighted-Average Exercise Price for Equity
Outstanding, Beginning balance	$ 1.60
Exercised	1.14
Forfeited and cancelled	5.47
Outstanding, Ending balance	2.35	$ 1.60
Options exercisable	$ 1.58
Weighted-Average Contractual Life (In Years)
Outstanding	5 years 10 months 24 days	6 years
Options exercisable	5 years 8 months 12 days
Aggregate Intrinsic Value
Outstanding, Beginning balance	$ 143,059
Exercised	111,227	$ 2,238	$ 2,021
Outstanding, Ending balance	56,716	$ 143,059
Options exercisable	$ 48,928

Stock-based Compensation - Summary of Restricted Stock Unit Activity (Details) - RSUs - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Shares
Unvested outstanding, beginning balance	2,372,380
Granted	1,917,043
Vested	(1,087,279)	(693,922)	0
Cancelled	(229,142)
Unvested outstanding, ending balance	2,973,002	2,372,380
Weighted-Average Grant Date Fair Value
Unvested outstanding, beginning balance	$ 12.34
Granted	35.79	$ 16.99	$ 3.89
Vested	14.71
Cancelled	19.46
Unvested outstanding, ending balance	$ 26.06	$ 12.34
Aggregate Intrinsic Value
Unvested outstanding, beginning balance	$ 71,124
Unvested outstanding, ending balance	$ 100,279	$ 71,124

Stock-based Compensation - Summary of Stock-based Compensation Expense by Award Type (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 20,794	$ 5,028	$ 322
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	247	281	$ 322
RSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 20,547	$ 4,747

Stock-based Compensation - Summary of Allocation of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 20,794	$ 5,028	$ 322
Cost of Revenue
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	354	151	18
Sales and Marketing Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	5,111	1,911	163
Product, Technology, and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	9,865	1,637	104
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 5,464	$ 1,329	$ 37

Stock-based Compensation - Summary of Shares of Common Stock Reserved for Future Issuance (Details)	Dec. 31, 2018 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares of authorized common stock reserved for future issuance	11,620,101
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares of authorized common stock reserved for future issuance	1,807,515
RSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares of authorized common stock reserved for future issuance	2,973,002
2017 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares of authorized common stock reserved for future issuance	6,839,584

Earnings Per Share - Additional Information (Details)		12 Months Ended
Earnings Per Share - Additional Information (Details)	Oct. 16, 2017 shares	Dec. 31, 2018 Vote shares	Dec. 31, 2017 shares
Earnings Per Share Basic [Line Items]
Convertible preferred stock, terms of conversion		On October 16, 2017, in connection with the closing of the IPO, all of the outstanding shares of convertible Preferred Stock automatically converted into 20,188,226 shares of Class A common stock and 40,376,452 shares of Class B common stock, the latter of which subsequently converted in full into shares of Class A common stock. As a result, there were no shares of Preferred Stock outstanding at the closing of the IPO and the Company has not issued any new shares of Preferred Stock since such closing.
Conversion of preferred stock	9,091,484
Preferred stock, shares outstanding		0	0
Conversion of stock, description		Each share of Class B common stock is convertible into one share of Class A common stock at the option of the holder at any time or automatically upon certain events described in the Company’s amended and restated certificate of incorporation, including on either the death or voluntary termination of the Company’s Chief Executive Officer.
Undistributed earnings ratio used to calculate allocation to class of stock		100.00%
IPO
Earnings Per Share Basic [Line Items]
Preferred stock, shares outstanding	0
Class A Common Stock
Earnings Per Share Basic [Line Items]
Conversion of preferred stock	60,564,678
Right to voting		one vote per share
Number of votes entitled to stockholders per share \| Vote		1
Conversion of stock		7,534,710
Class A Common Stock \| IPO
Earnings Per Share Basic [Line Items]
Conversion of preferred stock	20,188,226
Class B Common Stock
Earnings Per Share Basic [Line Items]
Conversion of preferred stock	40,376,452
Right to voting		ten votes per share
Number of votes entitled to stockholders per share \| Vote		10
Class of share converted to another class		one share of Class A common stock
Conversion of stock		1

Earnings Per Share - Schedule of Reconciliation of Numerator and Denominator Used in Calculation of Basic and Diluted Net (Loss) Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income	$ 12,450	$ 13,882	$ 33,343	$ 5,495	$ 2,267	$ 2,379	$ 4,346	$ 4,207	$ 65,170	$ 13,199	$ 6,497
Deemed dividend to preferred stockholders											(32,087)
Net income attributable to participating securities										(6,098)
Net income (loss) attributable to common stockholders — basic									65,170	7,101	(25,590)
Net income attributable to participating securities										(5,829)
Net income (loss) attributable to common stockholders — diluted									$ 65,170	$ 7,370	$ (25,590)
Denominator:
Weighted–average number of shares of common stock used in computing net income per share attributable to common stockholders — basic									108,833,028	55,835,265	44,138,922
Dilutive effect of share equivalents resulting from stock options									3,009,748	4,290,362
Dilutive effect of share equivalents resulting from unvested restricted stock units									1,521,936	511,957
Weighted–average number of shares of common stock used in computing net income per share — diluted									113,364,712	60,637,584	44,138,922
Net income (loss) per share attributable to common stockholders:
Basic	$ 0.11	$ 0.13	$ 0.31	$ 0.05	$ 0.02	$ 0.02	$ 0.04	$ 0.04	$ 0.60	$ 0.13	$ (0.58)
Diluted	$ 0.11	$ 0.12	$ 0.29	$ 0.05	$ 0.02	$ 0.02	$ 0.04	$ 0.04	$ 0.57	$ 0.12	$ (0.58)

Earnings Per Share - Schedule of Potentially Dilutive Common Stock Equivalents Excluded from Calculation of Diluted Weighted-average Shares Outstanding (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock Options Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive common stock equivalents excluded from calculation of diluted weighted-average shares outstanding			5,698,812
Restricted Stock Units Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive common stock equivalents excluded from calculation of diluted weighted-average shares outstanding	126,816	829	1,580,094
Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive common stock equivalents excluded from calculation of diluted weighted-average shares outstanding			10,094,108

Income Taxes - Schedule of Domestic and Foreign Components of Income Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments [Abstract]
United States	$ 24,426	$ 15,543	$ 8,919
Foreign	1,058	294	26
Income before income taxes	$ 25,484	$ 15,837	$ 8,945

Income Taxes - Schedule of (Benefit From) Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current (benefit) provision:
Federal	$ (860)	$ 3,262	$ 1,440
State	92	431	223
Foreign	122	62	3
Current (benefit) provision	(646)	3,755	1,666
Deferred (benefit) provision:
Federal	(27,675)	(755)	880
State	(11,499)	(343)	(98)
Foreign	134	(19)
Deferred (benefit) provision	(39,040)	(1,117)	782
Income tax (benefit) provision	$ (39,686)	$ 2,638	$ 2,448

Income Taxes - Schedule of Effective Tax Rates Less than US Federal Statutory Rate Primarily Due to Excess Tax Deductions (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]
U.S. federal taxes at statutory rate	21.00%	35.00%	35.00%
State taxes, net of federal benefit	(25.60%)	3.10%	4.50%
Nondeductible expenses	4.10%	1.20%	2.00%
Tax deductible IPO costs		(9.30%)
Stock compensation	(127.20%)	(4.40%)
Foreign rate differential	(0.40%)	(0.40%)	(0.10%)
Credits	(28.40%)	(9.00%)	(15.00%)
Other	0.70%	0.50%	1.00%
Total	(155.80%)	16.70%	27.40%

Income Taxes - Schedule of Income Tax Effect of Each Type of Temporary Difference and Carryforward (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 34,450
Credit carryforwards	6,562	$ 166
Stock-based compensation	1,945	1,301
Landlord allowance on leasehold improvements	1,908	1,078
Deferred rent	873	583
Accruals and reserves	1,074	606
Deferred tax assets	46,812	3,734
Deferred tax liability:
Prepaid expenses	(931)
Deferred commissions	(3,187)
Unbilled revenue	(227)
Fixed assets	(3,581)	(2,909)
Deferred tax liability	(7,926)	(2,909)
Net deferred tax assets	$ 38,886	$ 825

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Line Items]
U.S. federal corporate tax rate	21.00%	35.00%	35.00%
Provisional Income tax expense	$ 16,000
Tax expense recognized related to re-measurement of deferred tax balance	0	$ 151,000
Provisional amount for one-time transition tax liability for foreign subsidiaries	16,000	36,000
Provisional income tax expense, increase		36,000
Provisional amounts for GILTI		0
Deferred tax assets, federal net operating loss carryforwards	130,927,000
Deferred tax assets, state net operating loss carryforwards	$ 111,234,000
Percentage of annual limitation of taxable income	80.00%
State net operating loss carryforward, expiration year	2028
Tax credit carryforward, expiration year	2038
Liabilities for uncertain tax positions	$ 0	0
Accrued interest or penalties related to uncertain tax positions	0	$ 0
Federal
Income Tax Disclosure [Line Items]
Tax credit carryforwards	3,875,000
State
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 3,401,000
Internal Revenue Service (IRS)
Income Tax Disclosure [Line Items]
Tax credit carryforward limitations on use, cumulative ownership change, period	3 years
Tax credit carryforward, limitations on use	an ownership change, as defined by Section 382, results from transactions that increase the ownership of 5% stockholders in the stock of a corporation by more than 50% in the aggregate over a three-year period.
Internal Revenue Service (IRS) \| Minimum
Income Tax Disclosure [Line Items]
Tax credit carryforward limitations on use, cumulative ownership change percentage	5.00%
Internal Revenue Service (IRS) \| Maximum
Income Tax Disclosure [Line Items]
Tax credit carryforward limitations on use, cumulative ownership change percentage	50.00%
Internal Revenue Service (IRS) \| Federal
Income Tax Disclosure [Line Items]
Income tax examination year under examination	2016
Closed tax year	2014
Internal Revenue Service (IRS) \| State
Income Tax Disclosure [Line Items]
Closed tax year	2014
UK Revenue Agency \| Foreign
Income Tax Disclosure [Line Items]
Open tax year	2016
Canada Revenue Agency \| Foreign
Income Tax Disclosure [Line Items]
Open tax year	2016
Revenue Commissioners, Ireland \| Foreign
Income Tax Disclosure [Line Items]
Open tax year	2016

Segment and Geographic Information - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018 Segment
Segment Reporting Information [Line Items]
Number of reportable segments	2
United States \| Total Assets \| Geographic Concentration Risk
Segment Reporting Information [Line Items]
Concentration of credit risk, percentage	97.00%

Segment and Geographic Information - Summary of Operations by Segment and Geographical Area (Details) - USD ($)
$ in Thousands

3 Months Ended

12 Months Ended

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2017

Sep. 30, 2017

Jun. 30, 2017

Mar. 31, 2017

Dec. 31, 2018

^[1]

Dec. 31, 2017

Dec. 31, 2016

Segment revenue:

Segment income (loss) from operations:

$ 126,090

$ 119,125

$ 110,296

$ 98,575

$ 90,597

$ 82,989

$ 76,240

$ 67,035

$ 454,086

$ 316,861

$ 198,141

Total income from operations

$ 6,902

$ 5,877

$ 3,953

$ 6,459

$ 32

$ 2,863

$ 5,995

$ 6,384

23,191

15,274

8,571

United States

Segment revenue:

Segment income (loss) from operations:

437,166

307,472

195,824

Total income from operations

58,387

41,586

27,461

International

Segment revenue:

Segment income (loss) from operations:

16,920

9,389

2,317

Total income from operations

$ (35,196)

$ (26,312)

$ (18,890)

[1]	Included in the year ended December 31, 2018 United States and International segments are revenue adjustments of $94 and $32, respectively, and operating income adjustments of $8,613 and $811, respectively, related to the Company's adoption of ASC 606.

Segment and Geographic Information - Summary of Operations by Segment and Geographical Area (Parenthetical) (Details) - USD ($)
$ in Thousands

3 Months Ended

12 Months Ended

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2017

Sep. 30, 2017

Jun. 30, 2017

Mar. 31, 2017

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

$ 126,090

$ 119,125

$ 110,296

$ 98,575

$ 90,597

$ 82,989

$ 76,240

$ 67,035

$ 454,086

^[1]

$ 316,861

$ 198,141

$ 6,902

5,877

3,953

6,459

$ 32

$ 2,863

$ 5,995

$ 6,384

23,191

^[1]

15,274

8,571

United States

437,166

^[1]

307,472

195,824

58,387

^[1]

41,586

27,461

International

16,920

^[1]

9,389

2,317

(35,196)

^[1]

$ (26,312)

$ (18,890)

Adjustments | ASC 606

(29)

(126)

126

Adjustments | United States | ASC 606

$ 2,242

$ 2,509

$ 2,537

Adjustments | International | ASC 606

8,613

$ 811

[1]	Included in the year ended December 31, 2018 United States and International segments are revenue adjustments of $94 and $32, respectively, and operating income adjustments of $8,613 and $811, respectively, related to the Company's adoption of ASC 606.

Employee Benefit Plans - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Compensation And Retirement Disclosure [Abstract]
Employer matching contribution, percent of match	50.00%
Defined contribution plan, maximum annual contributions per employee, percent	6.00%
Annual maximum amount of employee contributions	$ 5,000,000
Defined contribution plan, employer contribution	$ 1,953,000	$ 724,000	$ 0

Quarterly Financial Results (Unaudited) - Schedule of Unaudited Quarterly Financial Information (Details) - USD ($)
$ / shares in Units, $ in Thousands

3 Months Ended

12 Months Ended

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2017

Sep. 30, 2017

Jun. 30, 2017

Mar. 31, 2017

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

Quarterly Financial Data [Abstract]

$ 126,090

$ 119,125

$ 110,296

$ 98,575

$ 90,597

$ 82,989

$ 76,240

$ 67,035

$ 454,086

^[1]

$ 316,861

$ 198,141

6,871

6,412

5,959

5,569

5,242

4,720

4,322

3,325

24,811

^[2]

17,609

^[2]

9,575

^[2]

119,219

112,713

104,337

93,006

85,355

78,269

71,918

63,710

429,275

299,252

188,566

6,902

5,877

3,953

6,459

2,863

5,995

6,384

23,191

^[1]

15,274

8,571

$ 12,450

$ 13,882

$ 33,343

$ 5,495

$ 2,267

$ 2,379

$ 4,346

$ 4,207

$ 65,170

$ 13,199

$ 6,497

$ 0.11

$ 0.13

$ 0.31

$ 0.05

$ 0.02

$ 0.04

$ 0.60

$ 0.13

$ (0.58)

$ 0.11

$ 0.12

$ 0.29

$ 0.05

$ 0.02

$ 0.04

$ 0.57

$ 0.12

$ (0.58)

[1]	Included in the year ended December 31, 2018 United States and International segments are revenue adjustments of $94 and $32, respectively, and operating income adjustments of $8,613 and $811, respectively, related to the Company's adoption of ASC 606.
[2]	Includes depreciation and amortization expense for the years ended December 31, 2018, 2017, and 2016 of $2,225 $1,140, and $438, respectively.

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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+ Details

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109260490&loc=SL5780133-109256

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(19))
-URI http://asc.fasb.org/extlink&oid=114873790&loc=SL114874131-224263

+ Details

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Quarterly Financial Results (Unaudited) - Schedule of Unaudited Quarterly Financial Information (Parenthetical) (Details) - USD ($)
$ / shares in Units, $ in Thousands

3 Months Ended

12 Months Ended

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2017

Sep. 30, 2017

Jun. 30, 2017

Mar. 31, 2017

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2016

$ 126,090

$ 119,125

$ 110,296

$ 98,575

$ 90,597

$ 82,989

$ 76,240

$ 67,035

$ 454,086

^[1]

$ 316,861

$ 198,141

6,871

6,412

5,959

5,569

5,242

4,720

4,322

3,325

24,811

^[2]

17,609

^[2]

9,575

^[2]

119,219

112,713

104,337

93,006

85,355

78,269

71,918

63,710

429,275

299,252

188,566

6,902

5,877

3,953

6,459

2,863

5,995

6,384

23,191

^[1]

15,274

8,571

$ 12,450

$ 13,882

$ 33,343

$ 5,495

$ 2,267

$ 2,379

$ 4,346

$ 4,207

$ 65,170

$ 13,199

$ 6,497

$ 0.11

$ 0.13

$ 0.31

$ 0.05

$ 0.02

$ 0.04

$ 0.60

$ 0.13

$ (0.58)

ASC 606 | Pro Forma as if the Previous Accounting Guidance was in Effect

$ 0.11

$ 0.12

$ 0.29

$ 0.05

$ 0.02

$ 0.04

$ 0.57

$ 0.12

$ (0.58)

$ 119,042

$ 110,325

$ 98,701

$ 453,960

6,412

5,959

5,569

24,811

112,630

104,366

93,132

429,149

3,635

1,444

3,922

13,767

$ 12,135

$ 31,265

$ 3,651

$ 58,182

$ 0.11

$ 0.29

$ 0.03

$ 0.53

$ 0.11

$ 0.28

$ 0.03

$ 0.51

ASC 606 | Adjustments

$ 83

$ (29)

$ (126)

$ 126

(29)

(126)

2,242

2,509

2,537

$ 1,747

$ 2,078

$ 1,844

$ 0.02

$ 0.07