Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2019
Feb. 06, 2020
Jun. 30, 2019
Document And Entity Information [Line Items]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2019    
Document Fiscal Year Focus 2019    
Document Fiscal Period Focus FY    
Entity Registrant Name CarGurus, Inc.    
Trading Symbol CARG    
Entity Central Index Key 0001494259    
Entity Well-known Seasoned Issuer Yes    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Interactive Data Current Yes    
Current Fiscal Year End Date --12-31    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     $ 2,464,065,369
Entity File Number 001-38233    
Title of 12(b) Security Class A Common Stock, par value $0.001 per share    
Security Exchange Name NASDAQ    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 04-3843478    
Entity Address, Address Line One 2 Canal Park    
Entity Address, Address Line Two 4th Floor    
Entity Address, City or Town Cambridge    
Entity Address, State or Province MA    
Entity Address, Postal Zip Code 02141    
City Area Code 617    
Local Phone Number 354-0068    
Document Annual Report true    
Document Transition Report false    
Documents Incorporated by Reference


Portions of the registrant’s definitive Proxy Statement for its 2020 Annual Meeting of Stockholders are incorporated by reference in Part III of this Annual Report on Form 10-K. Such Proxy Statement will be filed with the U.S. Securities and Exchange Commission within 120 days after the end of the fiscal year to which this report relates. Except with respect to information specifically incorporated by reference in this Form 10-K, the Proxy Statement is not deemed to be filed as part of this Form 10-K.

Class A Common Stock      
Document And Entity Information [Line Items]      
Entity Common Stock, Shares Outstanding   91,983,435  
Class B Common Stock      
Document And Entity Information [Line Items]      
Entity Common Stock, Shares Outstanding   20,314,644