CarGurus (CARG) 10-Q 9 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 04, 2021
Document And Entity Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Entity Registrant Name	CARGURUS, INC.
Trading Symbol	CARG
Entity Central Index Key	0001494259
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 Current Reporting Status	Yes
Entity File Number	001-38233
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
Entity Interactive Data Current	Yes
Document Quarterly Report	true
Document Transition Report	false
Entity Incorporation, State or Country Code	DE
Title of 12(b) Security	Class A Common Stock, par value $0.001 per share
Security Exchange Name	NASDAQ
Class A Common Stock
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		101,684,111
Class B Common Stock
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		15,999,173

Unaudited Condensed Consolidate

Unaudited Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets
Cash and cash equivalents	$ 231,091	$ 190,299
Investments	90,000	100,000
Accounts Receivable, after Allowance for Credit Loss, Current	85,182	18,235
Inventory	6,395
Prepaid expenses, prepaid income taxes and other current assets	13,183	12,385
Deferred contract costs	9,905	10,807
Restricted cash	5,753	250
Total current assets	441,509	331,976
Property and equipment, net	29,569	27,483
Intangible assets, net	92,421	10,862
Goodwill	155,707	29,129
Operating lease right-of-use assets	63,841	60,835
Restricted cash	10,377	10,377
Deferred tax assets	13,741	19,774
Deferred contract costs, net of current portion	6,866	9,189
Other non-current assets	5,886	2,673
Total assets	819,917	502,298
Current liabilities
Accounts payable	55,340	21,563
Accrued expenses, accrued income taxes and other current liabilities	21,922	24,751
Deferred revenue	12,517	9,137
Operating lease liabilities	12,671	11,085
Total current liabilities	102,450	66,536
Operating lease liabilities	61,013	58,810
Deferred tax liabilities	19	291
Other non–current liabilities	12,546	3,075
Total liabilities	176,028	128,712
Commitments and contingencies (Note 9)
Redeemable noncontrolling interest	54,633
Stockholders’ equity:
Additional paid-in capital	379,808	242,181
Retained earnings	209,024	129,412
Accumulated other comprehensive income	307	1,880
Total stockholders’ equity	589,256	373,586
Total liabilities, redeemable noncontrolling interest and stockholders’ equity	819,917	502,298
Class A Common Stock
Stockholders’ equity:
Common stock	101	94
Class B Common Stock
Stockholders’ equity:
Common stock	$ 16	$ 19

Unaudited Condensed Consolida_2

Unaudited Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Allowance for doubtful accounts	$ 602	$ 616
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Class A Common Stock
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	101,003,874	94,310,309
Common stock, shares outstanding	101,003,874	94,310,309
Class B Common Stock
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	16,470,842	19,076,500
Common stock, shares outstanding	16,470,842	19,076,500

Unaudited Condensed Consolida_3

Unaudited Condensed Consolidated Income Statements - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Revenue		$ 222,915	$ 147,472	$ 612,031	$ 399,898
Cost of revenue	[1]	60,033	9,762	134,408	31,252
Gross profit		162,882	137,710	477,623	368,646
Operating expenses:
Sales and marketing		66,626	57,618	200,935	189,796
Product, technology, and development		26,539	20,758	79,333	65,729
General and administrative		20,414	14,279	67,095	44,297
Depreciation and amortization		9,227	1,488	25,916	4,529
Total operating expenses		122,806	94,143	373,279	304,351
Income from operations		40,076	43,567	104,344	64,295
Other income, net		143	205	426	1,407
Income before income taxes		40,219	43,772	104,770	65,702
Provision for income taxes		10,952	11,209	28,556	13,312
Consolidated net income		29,267	32,563	76,214	52,390
Net income (loss) attributable to redeemable noncontrolling interest		68		(3,398)
Net income attributable to common stockholders		$ 29,199	$ 32,563	$ 79,612	$ 52,390
Net income per share attributable to common stockholders: (Note 11)
Basic		$ 0.25	$ 0.29	$ 0.68	$ 0.46
Diluted		$ 0.24	$ 0.29	$ 0.66	$ 0.46
Weighted-average number of shares of common stock used in computing net income per share attributable to common stockholders:
Basic		117,412,164	113,027,995	116,955,188	112,707,003
Diluted		120,438,373	113,966,863	119,051,228	113,732,616
[1]	Includes depreciation and amortization expense for the three months ended September 30, 2021 and 2020 and for the nine months ended September 30, 2021 and 2020 of $ 1,429 , $ 944 , $ 3,571 , and $ 4,250 , respectively.

Unaudited Condensed Consolida_4

Unaudited Condensed Consolidated Income Statements (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Depreciation and amortization expense	$ 1,429	$ 944	$ 3,571	$ 4,250

Unaudited Condensed Consolida_5

Unaudited Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Consolidated net income	$ 29,267	$ 32,563	$ 76,214	$ 52,390
Other comprehensive income (loss):
Foreign currency translation adjustment	(738)	1,013	(1,573)	1,001
Consolidated comprehensive income	28,529	33,576	74,641	53,391
Less comprehensive income (loss) attributable to redeemable noncontrolling interests	68		(3,398)
Comprehensive income attributable to common stockholders	$ 28,461	$ 33,576	$ 78,039	$ 53,391

Unaudited Condensed Consolida_6

Unaudited Condensed Consolidated Statements of Redeemable Noncontrolling Interest and Stockholders' Equity - USD ($) $ in Thousands	Total	Class A Common Stock	Class B Common Stock	Common StockClass A Common Stock	Common StockClass B Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2019	$ 256,855			$ 92	$ 20	$ 205,234	$ 51,859	$ (350)
Beginning balance, Shares at Dec. 31, 2019				91,819,649	20,314,644
Net income (loss)	12,696						12,696
Stock–based compensation expense	11,793					11,793
Issuance of common stock upon exercise of stock options	514					514
Issuance of common stock upon exercise of stock options, Shares				160,668
Issuance of common stock upon vesting of restricted stock units				$ 1		(1)
Issuance of common stock upon vesting of restricted stock units, Shares				308,303
Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options	(3,397)					(3,397)
Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options, Shares				(106,934)
Conversion of common stock, shares issued				335,741
Conversion of common stock, shares converted					(335,741)
Foreign currency translation adjustment	(493)							(493)
Ending balance at Mar. 31, 2020	277,968			$ 93	$ 20	214,143	64,555	(843)
Ending balance, Shares at Mar. 31, 2020				92,517,427	19,978,903
Beginning balance at Dec. 31, 2019	256,855			$ 92	$ 20	205,234	51,859	(350)
Beginning balance, Shares at Dec. 31, 2019				91,819,649	20,314,644
Net income (loss)	52,390
Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options, Shares		(337,313)
Foreign currency translation adjustment	1,001
Ending balance at Sep. 30, 2020	338,259			$ 94	$ 19	233,246	104,249	651
Ending balance, Shares at Sep. 30, 2020				94,016,568	19,076,500
Beginning balance at Mar. 31, 2020	277,968			$ 93	$ 20	214,143	64,555	(843)
Beginning balance, Shares at Mar. 31, 2020				92,517,427	19,978,903
Net income (loss)	7,131						7,131
Stock–based compensation expense	12,249					12,249
Issuance of common stock upon exercise of stock options	415					415
Issuance of common stock upon exercise of stock options, Shares				84,796
Issuance of common stock upon vesting of restricted stock units, Shares				375,645
Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options	(2,389)					(2,389)
Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options, Shares		(119,009)
Conversion of common stock, shares issued				3,748
Conversion of common stock, shares converted					(3,748)
Foreign currency translation adjustment	481							481
Ending balance at Jun. 30, 2020	295,855			$ 93	$ 20	224,418	71,686	(362)
Ending balance, Shares at Jun. 30, 2020				92,862,607	19,975,155
Net income (loss)	32,563						32,563
Stock–based compensation expense	11,684					11,684
Issuance of common stock upon exercise of stock options	66					66
Issuance of common stock upon exercise of stock options, Shares				31,523
Issuance of common stock upon vesting of restricted stock units, Shares				335,153
Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options	(2,922)					(2,922)
Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options, Shares		(111,370)		(111,370)
Conversion of common stock				$ 1
Conversion of common stock, shares issued				898,655
Conversion of common stock, shares converted					(898,655)
Conversion of common stock, value					$ (1)
Foreign currency translation adjustment	1,013							1,013
Ending balance at Sep. 30, 2020	338,259			$ 94	$ 19	233,246	104,249	651
Ending balance, Shares at Sep. 30, 2020				94,016,568	19,076,500
Beginning balance at Dec. 31, 2020	373,586			$ 94	$ 19	242,181	129,412	1,880
Beginning balance, Shares at Dec. 31, 2020		94,310,309	19,076,500	94,310,309	19,076,500
Net income (loss)	22,361						22,361
Redeemable Noncontrolling Interest, Net income (loss)	(2,810)
Stock–based compensation expense	14,929					14,929
Issuance of common stock upon exercise of stock options	258					258
Issuance of common stock upon exercise of stock options, Shares				93,455
Issuance of common stock upon vesting of restricted stock units				$ 1		(1)
Issuance of common stock upon vesting of restricted stock units, Shares				473,883
Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options	(5,041)					(5,041)
Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options, Shares				(162,950)
Conversion of common stock				$ 1
Conversion of common stock, shares issued				929,597
Conversion of common stock, shares converted					(929,597)
Conversion of common stock, value					$ (1)
Issuance of common stock upon for acquisition	103,645			$ 3		103,642
Issuance of common stock upon for acquisition, Shares				3,115,282
Acquisition of a 51% interest in CarOffer, LLC	58,031
Foreign currency translation adjustment	(1,083)							(1,083)
Ending balance at Mar. 31, 2021	508,655			$ 99	$ 18	355,968	151,773	797
Redeemable Noncontrolling Interest, Ending balance at Mar. 31, 2021	55,221
Ending balance, Shares at Mar. 31, 2021				98,759,576	18,146,903
Beginning balance at Dec. 31, 2020	373,586			$ 94	$ 19	242,181	129,412	1,880
Beginning balance, Shares at Dec. 31, 2020		94,310,309	19,076,500	94,310,309	19,076,500
Net income (loss)	79,612
Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options, Shares		(404,626)
Foreign currency translation adjustment	(1,573)
Ending balance at Sep. 30, 2021	589,256			$ 101	$ 16	379,808	209,024	307
Redeemable Noncontrolling Interest, Ending balance at Sep. 30, 2021	54,633
Ending balance, Shares at Sep. 30, 2021		101,003,874	16,470,842	101,003,874	16,470,842
Beginning balance at Mar. 31, 2021	508,655			$ 99	$ 18	355,968	151,773	797
Redeemable Noncontrolling Interest, Beginning balance at Mar. 31, 2021	55,221
Beginning balance, Shares at Mar. 31, 2021				98,759,576	18,146,903
Net income (loss)	28,052						28,052
Redeemable Noncontrolling Interest, Net income (loss)	(656)
Stock–based compensation expense	15,253					15,253
Issuance of common stock upon exercise of stock options	140					140
Issuance of common stock upon exercise of stock options, Shares				36,027
Issuance of common stock upon vesting of restricted stock units, Shares				391,468
Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options	(3,167)					(3,167)
Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options, Shares				(126,703)
Foreign currency translation adjustment	248							248
Ending balance at Jun. 30, 2021	549,181			$ 99	$ 18	368,194	179,825	1,045
Redeemable Noncontrolling Interest, Ending balance at Jun. 30, 2021	54,565
Ending balance, Shares at Jun. 30, 2021				99,060,368	18,146,903
Net income (loss)	29,199						29,199
Redeemable Noncontrolling Interest, Net income (loss)	68
Stock–based compensation expense	14,581					14,581
Issuance of common stock upon exercise of stock options	139					139
Issuance of common stock upon exercise of stock options, Shares				43,909
Issuance of common stock upon vesting of restricted stock units, Shares				338,509
Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options	(3,106)					(3,106)
Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options, Shares		(114,973)		(114,973)
Conversion of common stock				$ 2
Conversion of common stock, shares issued				1,676,061
Conversion of common stock, shares converted					(1,676,061)
Conversion of common stock, value					$ (2)
Foreign currency translation adjustment	(738)							(738)
Ending balance at Sep. 30, 2021	589,256			$ 101	$ 16	$ 379,808	$ 209,024	$ 307
Redeemable Noncontrolling Interest, Ending balance at Sep. 30, 2021	$ 54,633
Ending balance, Shares at Sep. 30, 2021		101,003,874	16,470,842	101,003,874	16,470,842

Unaudited Condensed Consolida_7

Unaudited Condensed Consolidated Statements of Redeemable Noncontrolling Interest and Stockholders' Equity (Parenthetical)	Sep. 30, 2021	Mar. 31, 2021	Jan. 14, 2021
Car Offer
Business acquisition, percentage of interest acquired	51.00%	51.00%	51.00%

Unaudited Condensed Consolida_8

Unaudited Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating Activities
Consolidated net income	$ 76,214	$ 52,390
Adjustments to reconcile consolidated net income to net cash provided by operating activities:
Depreciation and amortization	29,487	8,779
Currency gain on foreign denominated transactions	(72)	(32)
Deferred taxes	5,774	14,769
Provision for doubtful accounts	727	1,742
Stock-based compensation expense	42,551	34,403
Amortization of deferred contract costs	9,643	8,595
Impairment of website development costs	2,351
Changes in operating assets and liabilities:
Accounts receivable, net	(51,595)	5,954
Inventory	(4,057)
Prepaid expenses, prepaid income taxes, and other assets	(2,970)	7,104
Deferred contract costs	(6,522)	(6,922)
Accounts payable	24,548	(19,745)
Accrued expenses, accrued income taxes, and other liabilities	4,808	1,726
Deferred revenue	3,390	(313)
Lease obligations	786	356
Net cash provided by operating activities	135,063	108,806
Investing Activities
Purchases of property and equipment	(4,935)	(2,732)
Capitalization of website development costs	(4,145)	(3,045)
Cash paid for acquisitions, net of cash acquired	(64,273)	(21,056)
Investments in certificates of deposit	(90,000)
Maturities of certificates of deposit	100,000	111,692
Net cash (used in) provided by investing activities	(63,353)	84,859
Financing Activities
Proceeds from exercise of stock options	537	995
Payment of finance lease obligations	(29)	(28)
Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options	(11,314)	(8,708)
Repayment of line of credit	(14,250)
Net cash used in financing activities	(25,056)	(7,741)
Impact of foreign currency on cash, cash equivalents, and restricted cash	(359)	171
Net increase in cash, cash equivalents, and restricted cash	46,295	186,095
Cash, cash equivalents, and restricted cash at beginning of period	200,926	70,723
Cash, cash equivalents, and restricted cash at end of period	247,221	256,818
Supplemental disclosure of cash flow information:
Cash paid for income taxes	21,798	875
Unpaid purchases of property and equipment and and internal-use software	504	165
Capitalized stock-based compensation expense in website development and internal-use software costs	2,212	1,323
Cash paid for operating lease liabilities	12,320	$ 10,329
Obtaining a right-of-use asset in exchange for a finance lease liability	664
Obtaining a right-of-use asset in exchange for an operating lease liability	12,336
Issuance of stock for acquisition	$ 103,645

Organization and Business Descr

Organization and Business Description	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Organization and Business Description	1. Organization and Business Description CarGurus, Inc. (the “Company”) is a multinational, online automotive platform for buying and selling vehicles that is building upon its industry-leading listings marketplace with both digital retail solutions and the CarOffer online wholesale platform. The CarGurus marketplace gives consumers the confidence to purchase or sell a vehicle either online or in-person; and gives dealerships the power to accurately price, effectively market, instantly acquire and quickly sell vehicles, all with a nationwide reach. The Company uses proprietary technology, search algorithms and data analytics to bring trust, transparency and competitive pricing to the automotive shopping experience. The Company is headquartered in Cambridge, Massachusetts and was incorporated in the State of Delaware on June 26, 2015 . The Company operates principally in the United States. In the United States, it also operates as independent brands the Autolist online marketplace, which it wholly owns, and the CarOffer , LLC (“CarOffer”) digital wholesale marketplace, in which it has a 51 % interest. In addition to the United States, the Company operates online marketplaces under the CarGurus brand in Canada and the United Kingdom. In the United Kingdom, it also operates as an independent brand the PistonHeads online marketplace, which it wholly owns. The Company also operated online marketplaces in Germany, Italy, and Spain until it ceased the operations of each of these marketplaces in the second quarter of 2020. The Company has subsidiaries in the United States, Canada, Ireland, and the United Kingdom. Additionally, it has two reportable segments, United States and International. See Note 13 of the Unaudited Condensed Consolidated Financial Statements included elsewhere in this Quarterly Report.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying interim condensed consolidated financial statements (the “Unaudited Condensed Consolidated Financial Statements”) are unaudited. The Unaudited Condensed Consolidated Financial Statements and related disclosures 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 GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). The Unaudited Condensed Consolidated Financial Statements have also been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Accordingly, certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. The Unaudited Condensed Consolidated Financial Statements reflect all adjustments, consisting of only normal recurring adjustments, necessary for the fair presentation of the Company’s financial position as of September 30, 2021 and December 31, 2020, results of operations, comprehensive income, changes in shareholders’ equity for the three and nine months ended September 30, 2021 and 2020 and cash flows for the nine months ended September 30, 2021 and 2020. These interim period results are not necessarily indicative of the results to be expected for any other interim period or the full year. The Unaudited Condensed Consolidated Financial Statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020, filed with the SEC on February 12, 2021 (the “Annual Report”). While the Company disclosed other non-current liabilities separately in the Company's Quarterly Report on Form 10-Q for the quarter ended September 30, 2020, filed with the SEC on November 5, 2020, the accompanying Unaudited Condensed Consolidated Statements of Cash Flows for the nine months ended September 30, 2020 present other non-current liabilities with accrued expenses, accrued income taxes and other current liabilities to conform to the current year presentation, as other non-current liabilities did not meet the threshold for separate disclosure. Principles of Consolidation The accompanying Unaudited Condensed Consolidated Financial Statements include the accounts of the Company and its subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Subsequent Event 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 for certain estimates or to identify matters that require additional disclosure. The Company has evaluated all subsequent events and determined that there are no material recognized or unrecognized subsequent events requiring disclosure. Use of Estimates The preparation of the Unaudited Condensed Consolidated Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, and the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. Although the Company regularly assesses these estimates, actual results could differ materially from these estimates. 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. Changes in estimates are recorded in the period in which they become known. Significant estimates relied upon in preparing the Unaudited Condensed Consolidated Financial Statements include the determination of sales allowance and variable consideration in the Company’s revenue recognition, allowance for doubtful accounts, the valuation of a redeemable noncontrolling interest, the valuation of equity and liability-classified compensation awards under ASC 718, the expensing and capitalization of product, technology, and development costs for website development and internal‑use software, the valuation and recoverability of goodwill and intangible assets and other long-lived assets, and the recoverability of the Company’s net deferred tax assets and related valuation allowance. Accordingly, the Company considers these to be its critical accounting policies, and believes that of the Company’s significant accounting policies, these policies involve the greatest degree of judgment and complexity. 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, cash equivalents, and investments with multiple financial institutions, its deposits may often exceed governmental 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 three and nine months ended September 30, 2021 and 2020 , no individual customer accounted for more than 10% of total revenue. As of September 30, 2021 , two customers accounted for 30 % and 15 % of net accounts receivable, respectively. As of December 31, 2020 , one customer accounted for approximately 10 % of net accounts receivable. Included in net accounts receivable at September 30, 2021 and December 31, 2020 are $ 6,694 and $ 7,426 , respectively, of unbilled accounts receivable relating primarily to advertising customers billed in a period subsequent to services rendered. Significant Accounting Policies The Unaudited Condensed Consolidated Financial Statements reflect the application of certain significant accounting policies as described below and elsewhere in these notes to the Unaudited Condensed Consolidated Financial Statements. As of September 30, 2021 , the Company’s significant accounting policies and estimates, which are detailed in the Annual Report, have not changed, other than those impacted by the acquisition of a 51 % interest in CarOffer and recently issued equity awards, as described below. Redeemable Noncontrolling Interest In connection with the Company’s acquisition of a 51 % interest in CarOffer on January 14, 2021, the Company became a party with the noncontrolling equity holders of CarOffer to the CarOffer Operating Agreement (as defined in Note 4 of the Unaudited Condensed Consolidated Financial Statements included elsewhere in this Quarterly Report), which, among other matters, sets forth certain put and call rights described in Note 4 of the Unaudited Condensed Consolidated Financial Statements included elsewhere in this Quarterly Report. The CarOffer Operating Agreement provides the Company with the right to purchase, and the noncontrolling equity holders with the right to sell to the Company, the noncontrolling CarOffer equity holders’ equity interests in CarOffer at a contractually defined formulaic purchase price, which is based on a multiple of earnings. As the purchase is contingently redeemable at the option of the noncontrolling equity holders, the Company classifies the carrying amount of the redeemable noncontrolling interests in the mezzanine section on the Unaudited Condensed Consolidated Balance Sheet, which is presented above the equity section and below the liabilities section. As of the date of Closing (as defined in Note 4 of the Unaudited Condensed Consolidated Financial Statements included elsewhere in this Quarterly Report), the noncontrolling interest was recognized at fair value computed using the Least Square Monte Carlo Simulation approach. Significant inputs to the model include market price of risk, volatility, correlation and risk-free rate. Subsequent to the Company’s acquisition of the 51 % interest on January 14, 2021, the redeemable noncontrolling interest is measured at the greater of the amount that would be paid if settlement occurred as of the balance sheet date based on the contractually defined redemption value and its carrying amount adjusted for net income (loss) attributable to the noncontrolling interest. Adjustments to the carrying value of the redeemable noncontrolling interest resulting from changes in the redemption value are recorded through retained earnings in the Unaudited Condensed Consolidated Balance Sheet. Revenue Recognition – Wholesale and Other Revenue and Inventory The Company generates wholesale and other revenue primarily from revenue relating to the wholesale sale of automobiles, display advertising revenue from auto manufacturers and other auto-related brand advertisers and revenue from partnerships with financing services companies. CarOffer revenue is comprised entirely of wholesale revenue. Wholesale revenue includes transaction fees earned by CarOffer from facilitating the purchase and sale of vehicles between dealers, where CarOffer collects fees from both the buyer and seller. CarOffer also sells vehicles to dealers that CarOffer acquires at other marketplaces or directly from consumers – in these instances, CarOffer collects a transaction fee from the buyer. CarOffer also charges the buyer fees to perform inspection and transportation services for all wholesale transactions. For facilitating the purchase and sale of vehicles between dealers, CarOffer generally does not control the vehicle and therefore acts as an agent in the transaction. Revenue earned from the fees for facilitating these transactions is recognized at a point in time when the vehicle is sold and revenue is recognized on a net basis. For vehicles sold to dealers that are acquired at other marketplaces, CarOffer generally does not control the vehicle and therefore acts as an agent in the transaction. Revenue earned from the fees for facilitating these transactions is recognized at a point in time when the vehicle is sold and revenue is typically recognized on a net basis. In these situations, the inventory is recorded on the balance sheet for the short period of time CarOffer possesses the vehicle title and is valued at the lower of cost or net realizable value. For vehicles sold to dealers that are acquired directly from consumers, CarOffer is deemed to control the vehicle and therefore is deemed to be the principal in the transaction. Revenue earned from the fees for facilitating these transactions is recognized point in time when the vehicle is sold and revenue is recognized on a gross basis. In these situations, the inventory is recorded on the balance sheet and is valued at the lower of cost or net realizable value. In certain circumstances, the vehicle may be arbitrated. For the majority of arbitrations, the vehicle is rematched to new buyers. In these situations, CarOffer is not deemed to control the vehicle and therefore is deemed to be an agent in the transaction. Revenue earned from the fees for facilitating these transactions is recognized at a point in time when the vehicle is sold and revenue is recognized on a net basis. In other limited situations, during an arbitration process, CarOffer acquires vehicles in transactions for which it is deemed to control the vehicle and therefore is deemed to be the principal in the transaction. Revenue earned from the fees for facilitating these transactions is recognized point in time and revenue is recognized on a gross basis. In these limited situations, the inventory is recorded on the balance sheet and is valued at the lower of cost or net realizable value. For inspection and transportation services, CarOffer leverages a network of third-party inspection service providers and transportation carriers. CarOffer is deemed to control both inspection and transportation services as it is primarily responsible for fulfillment and therefore acts as a principal in the transaction. Revenue from fees for inspection services is recognized at the point in time when the inspection is performed and revenue from fees for transportation services is recognized over time as delivery is completed. Revenue from both inspection and transportation services is recognized on a gross basis. Unearned revenue related to unsatisfied performance obligations is recorded as deferred revenue. Stock‑Based Compensation For stock‑based awards granted under the Company’s stock‑based compensation plans, the fair value of each award is determined on the date of grant. For restricted stock units (“RSUs”) granted subject to service-based vesting conditions, the fair value is determined based on the closing price of the Company’s Class A common stock , par value $ 0.001 per share (the “Class A common stock”), as reported on the Nasdaq Global Select Market on the date of grant. RSUs granted subject to service-based vesting conditions generally vest over a four-year requisite service period. For RSUs granted subject to market-based vesting conditions, the fair value is determined using the Monte Carlo simulation lattice model. The determination of the fair value using this model is affected by the Company’s stock price performance relative to the companies listed on the S&P 500 as of December 31, 2020 and a number of assumptions including volatility, correlation coefficient, risk-free interest rate and expected dividends. RSUs granted subject to market-based vesting conditions vest upon achievement of specified levels of market conditions . For stock options granted, the fair value is determined on the date of grant using the Black‑Scholes option‑pricing model. The determination of the fair value is affected by the Company’s stock price and a number of assumptions including volatility, term, risk-free interest rate and dividend yield. Stock options granted generally have a term of ten years from the date of grant and generally vest over a four-year requisite service period. In connection with the Company’s acquisition of a 51 % interest in CarOffer, the then-outstanding unvested incentive units (“CO Incentive Units”) of CarOffer and unvested Class CO CarOffer units (“the Subject Units”) remained outstanding and will vest over the requisite service periods as discussed below. Grants of the CO Incentive Units are subject to the CarOffer 2020 Equity Incentive Plan, adopted effective November 24, 2020 (the “2020 CO Plan”) , the applicable award agreement, and the CarOffer Operating Agreement . Following the Company’s acquisition of the 51 % interest in CarOffer on January 14, 2021, remaining unvested incentive interests will vest over a period of three ( 3 ) years, one third each on the first, second, and third anniversaries of January 14, 2021, provided that a grantee’s continuous service to CarOffer has not terminated on the applicable vesting date. Under the terms of the grants, vesting of unvested incentive interests is accelerated in the event of (i) a change of control of CarOffer (which, for the avoidance of doubt, does not include the Company’s acquisition of the 51 % interest on January 14, 2021), (ii) the death or disability of the grantee, (iii) termination of the grantee’s employment with CarOffer without cause, or (iv) termination of grantee’s employment by the grantee for good reason. Upon termination of a grantee’s continuous service to CarOffer voluntarily by the grantee (other than for good reason) or by CarOffer for cause, all of such grantee’s unvested incentive interests are forfeited. In addition, if a grantee’s continuous service terminates, then CarOffer has the option to repurchase any outstanding incentive interests from the grantee. In addition to the 2020 CO Plan, on December 9, 2020 CarOffer entered into a Vesting Agreement (the “Vesting Agreement”) regarding the vesting of CarOffer equity interests beneficially owned by Bruce Thompson, the founder and CEO of CarOffer, and certain affiliated persons (the “T5 Holders”) in connection with the Company’s then-anticipated acquisition of a 51 % interest in CarOffer. Pursuant to the Vesting Agreement, 432,592 Subject Units beneficially owned by the T5 Holders will vest in three (3) equal installments on the first, second, and third anniversary of the closing of the CarOffer Acquisition. As more particularly described in the Vesting Agreement, unvested Subject Units are subject to forfeiture in the event that Mr. Thompson’s relationship with CarOffer terminates other than in the event of a termination without cause (as defined in the Vesting Agreement) or due to Mr. Thompson’s death or disability. The Vesting Agreement also provides for acceleration of any unvested Subject Units in the event of the termination of Mr. Thompson’s employment with CarOffer without cause, Mr. Thompson’s death or disability, or the consummation of an eligible liquidity event (as defined in the Vesting Agreement). In connection with the Closing of the Company’s acquisition of the 51 % interest in CarOffer , CarOffer reserved 228,571 incentive units (the "2021 Incentive Units") for purposes of establishing an employee incentive equity plan. Thereafter, CarOffer formed CarOffer Incentive Equity, LLC (“CIE”), a Delaware manager-managed limited liability company managed by the Company, and established the CIE 2021 Equity Incentive Plan (the “2021 CO Plan). The 2021 CO Plan and related documentation, including the applicable award agreement, a vesting agreement between CarOffer and CIE, and the CarOffer Operating Agreement, provide for an incentive equity grant structure whereby 2021 Incentive Units will be granted to CIE and 2021 CO Plan grantees will receive an associated equity interest in CIE (the “CIE Interest”), with back-to-back vesting between the 2021 Incentive Units and the associated CIE Interest. Subject to any modifications as may be approved by the CarOffer Board of Managers in its discretion, grants under the 2021 CO Plan will vest over a period of three ( 3 ) years from the grant date, one third each on the first, second, and third anniversaries of the applicable grant date, provided that a grantee’s continuous service to CarOffer has not terminated on the applicable grant date. Upon termination of a grantee’s continuous service to CarOffer, all of such grantee’s unvested 2021 Incentive Units are forfeited. As of September 30, 2021 there had not been any grants of 2021 Incentive Units under the 2021 CO Plan. CO Incentive Units, Subject Units and 2021 Incentive Units are liability-classified awards because the awards can be put to the Company at a formula price such that the holders do not bear the risks and rewards associated with equity ownership . For liability-classified awards, the fair value is determined on the date of issuance using a Least Square Monte Carlo simulation model. The determination of the fair value is affected by CarOffer’s equity value, EBITDA, Excess Parent Capital (as defined in the CarOffer Operating Agreement), and revenue forecasts that drive the exercise price of future call/put rights, as well as a number of assumptions including market price of risk, volatility, correlation, and risk-free interest rate. Liability-classified awards are remeasured to fair value each period until settlement. The Company issues shares for RSUs and stock option exercises out of its shares available for issuance. The Company issues CO Incentive Units out of CarOffer’s units available for issuance. The Company accounts for forfeitures when they occur. The Company recognizes compensation expense 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. The tax effect of differences between tax deductions related to stock compensation and the corresponding financial statement expense compensation are recorded to tax expense. Excess tax benefits recognized on stock‑based compensation expense are classified as an operating activity in the Unaudited Condensed Consolidated Statements of Cash Flows. Recent Accounting Pronouncements Adopted Income Taxes In December 2019, the FASB issued ASU 2019-12, Income Taxes – Simplifying the Accounting for Income Taxes (“ASU 2019-12”). ASU 2019-12 simplifies the accounting for income taxes by removing several exceptions in the current standard and adding guidance to reduce complexity in certain areas, such as requiring that an entity reflect the effect of an enacted change in tax laws or rates in the annual effective tax rate computation in the interim period that includes the enactment date. The standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020, with early adoption permitted. The Company adopted the guidance on January 1, 2021 . The adoption did no t have an impact on the Unaudited Condensed Consolidated Financial Statements. 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. As of September 30, 2021, there are no new accounting pronouncements that the Company is considering adopting.

Revenue Recognition

Revenue Recognition	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Revenue Recognition	3. Revenue Recognition Revenue Recognition The following table summarizes revenue from contracts with customers by geographical region and by revenue source for the three and nine months ended September 30, 2021 and 2020. Three Months Ended Nine Months Ended 2021 2020 2021 2020 United States Marketplace subscription revenue $ 134,261 $ 121,814 $ 400,377 $ 330,295 Wholesale and other revenue 77,293 16,598 180,772 45,869 Total 211,554 138,412 581,149 376,164 International Marketplace subscription revenue 10,328 8,139 28,017 21,477 Wholesale and other revenue 1,033 921 2,865 2,257 Total 11,361 9,060 30,882 23,734 Total Revenue Marketplace subscription revenue 144,589 129,953 428,394 351,772 Wholesale and other revenue 78,326 17,519 183,637 48,126 Total $ 222,915 $ 147,472 $ 612,031 $ 399,898 The Company provides disaggregation of revenue based on the marketplace subscription versus wholesale and other revenue classification and based on geographic region in the table above as it believes these categories best depict how the nature, amount, timing and uncertainty of revenue and cash flows are affected by economic factors. ASC Topic 606, Revenue from Contracts with Customers (“Topic 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 the relevant quarter end. For contracts with an original expected duration greater than one year, the aggregate amount of the transaction price allocated to the performance obligations that were unsatisfied as of September 30, 2021 was approximately $ 12.2 million, which the Company expects to recognize over the next 12 months. For contracts with an original expected duration of one year or less, the Company has applied the practical expedient available under Topic 606 to not disclose the amount of transaction price allocated to unsatisfied performance obligations as of September 30, 2021. For performance obligations not satisfied as of September 30, 2021, and to which this expedient applies, 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 September 30, 2021. Revenue recognized during the three months ended September 30, 2021 and 2020 and the nine months ended September 30, 2021 and 2020, from amounts included in deferred revenue at the beginning of the period, was approximately $ 13,120 , $ 8,195 , $ 9,137 and $ 9,984 , respectively. In response to the COVID-19 pandemic, the Company reduced the subscription fees for paying dealers by at least 50 % on all marketplace subscriptions for the April and May 2020 service periods, as well as provided a fee reduction on all June 2020 marketplace subscriptions of 20 % for paying dealers in the United States and Canada and 50 % for paying dealers in the United Kingdom. These fee reductions resulted in a modification to contracts with initial contractual periods greater than one month. For any contract modified, the Company calculated the remaining transaction price and allocated the consideration over the remaining performance obligations. The Company also waived subscription fees for paying dealers in the United Kingdom for the December 2020 and February 2021 service periods. These fee reductions are included in the Company’s variable consideration assessment. The fee reductions had an immaterial impact on the Company’s revenues for the three and nine months ended September 30, 2021, as well as the three months ended September 30, 2020. The fee reductions had a material impact on the Company’s revenues for the nine months ended September 30, 2020.

Acquisitions

Acquisitions	9 Months Ended
	Sep. 30, 2021
Business Combinations [Abstract]
Acquisitions	4. Acquisitions On January 14, 2021 , the Company acquired a 51 % interest in CarOffer, which provides an automated instant vehicle trade platform and is based in Addison, Texas, pursuant to the terms of a Membership Interest Purchase Agreement (the “Purchase Agreement”) dated as of December 9, 2020 (the “Agreement Date”), as amended, by and among the Company, CarOffer, CarOffer Investors Holding, LLC, a Delaware limited liability company (“TopCo”), each of the Members of TopCo (the “Members”), and Bruce T. Thompson, an individual residing in Texas (the “Members’ Representative”). This acquisition (the “CarOffer Acquisition”) is intended to add wholesale vehicle purchasing and selling capabilities to CarGurus’ portfolio of dealer offerings and create a complete and efficient digital solution for dealers to sell and acquire vehicles at both retail and wholesale. Upon consummation of the transactions contemplated by the Purchase Agreement (the “Closing”), the Company acquired a 51 % interest in CarOffer for an aggregate consideration of $ 173,155 (the “Total Consideration”), such Total Consideration consisting of (a) shares of Class A common stock in the aggregate amount of $ 103,645 (the “Stock Consideration”) and (b) $ 69,510 in cash (the “Cash Consideration”). The number of shares of Class A common stock issued following the Closing in connection with the Stock Consideration was 3,115,282 , which was calculated by reference to a value of $ 22.51 per share, which equals the volume-weighted average closing price per share of Class A common stock on the Nasdaq Stock Market for the 28 consecutive trading days ending on the third Business Day (as defined in the Purchase Agreement) preceding the Agreement Date. Pursuant to the Purchase Agreement, the remaining equity in CarOffer (the “Remaining Equity”) is being retained by the then-current equity holders of CarOffer and subject to certain call and put arrangements discussed below. Pursuant to the Purchase Agreement, the Company established a retention pool in an aggregate amount of $ 8,000 in the form of RSUs to be issued pursuant to the Company’s standard form of RSU agreement under the 2017 Plan, (i) $ 6,000 of which was granted to certain CarOffer employees following the Closing in accordance with the terms of the Purchase Agreement and (ii) $ 2,000 of which is available for issuance to future CarOffer employees in accordance with the terms of the Purchase Agreement. RSUs issued from the retention pool will be subject to vesting based on rendering of future services. As of September 30, 2021, the Company incurred total acquisition-related costs of $ 2,647 related to the CarOffer Acquisition, of which $ 709 was incurred during the nine months ended September 30, 2021 and recorded as general and administrative operating expenses within the Unaudited Condensed Consolidated Income Statements. There were no acquisition-related costs incurred during the three months ended September 30, 2021. Acquisition-related costs were excluded from the purchase price allocation as they were primarily comprised of legal, professional and consulting expenses. The following table presents the total consideration transferred. Consideration Transferred Cash paid, net of cash acquired $ 64,273 Cash acquired 5,237 Cash consideration 69,510 Stock consideration 103,645 Total consideration transferred $ 173,155 The CarOffer Acquisition has been accounted for as a business combination under the acquisition method and, accordingly, the total consideration is allocated to the acquired assets and assumed liabilities. The Company’s 51 % interest in CarOffer represents a controlling financial interest in the entity as the minority interest holders only have protective rights such that CarOffer is consolidated as of the date of Closing. The following table presents the preliminary purchase price allocation recorded in the Company’s Unaudited Condensed Consolidated Balance Sheet as of the date of Closing, which is subject to finalization for estimates of the fair value of assets acquired and liabilities assumed as of the date of Closing, including, but not limited to tangible assets, intangible assets and tax-related items, and the related tax effects of any changes made: Adjusted Fair Cash and cash equivalents $ 5,237 Accounts receivable 16,119 Inventory 2,338 Prepaid expenses, prepaid income taxes and other current assets 95 Property and equipment, net 198 Intangible assets (1) 104,100 Goodwill (2) 127,500 Operating lease right-of-use assets 709 Accounts payable ( 8,888 ) Accrued expenses, accrued income taxes, and other current liabilities ( 15,513 ) Operating lease liabilities - current ( 230 ) Operating lease liabilities - non-current ( 479 ) Redeemable noncontrolling interest (3) ( 58,031 ) Total consideration transferred $ 173,155 (1) Identifiable definite-lived intangible assets were comprised of developed technology, brand, and customer relationships of $ 63,000 , $ 23,100 , and $ 18,000 , respectively, with estimated useful lives of 3 years, 11 years, and 3 years, respectively, which will be amortized on a straight-line basis over their estimated useful lives. The fair value of the developed technology has been estimated using the multi-period excess earnings method which is a variation of the income approach. The fair value of the brand and customer relationships has been estimated using the relief from royalty method and the with/without approach, respectively. (2) Goodwill represents the excess value of the purchase price over net assets acquired, primarily attributable to adding wholesale vehicle acquisition and selling capabilities to CarGurus’ portfolio of dealer offerings. All goodwill is assigned to the United States reporting segment. For tax purposes, $ 28,991 of the goodwill is deductible under IRC Section 197 upon finalization of the transaction cost study. In connection with the transaction, the Company accelerated certain stock options deemed to be outside of consideration transferred. Therefore, the Company recognized an additional $ 1,229 of stock-based compensation expense during the nine months ended September 30, 2021. (3) The fair value of the redeemable noncontrolling interest has been estimated using the Least Square Monte Carlo Simulation approach. Significant inputs include market price of risk, volatility, correlation and risk-free rate. In addition, the Company, TopCo, each Member and CarOffer MidCo, LLC, a Delaware limited liability company, entered into the Second Amended and Restated Limited Liability Company Agreement, dated as of December 9, 2020 (the “CarOffer Operating Agreement”), pursuant to which, among other matters, the Company secured the right to appoint a majority of the members of the Board of Managers of CarOffer, other rights customary for a transaction of this nature and the put and call rights described below. In the second half of 2022, the Company will have a call right (the “2022 Call Right”), exercisable in its sole discretion, to acquire a portion of the Remaining Equity representing up to twenty-five percent ( 25 %) of the fully diluted capitalization of CarOffer (such acquired Remaining Equity, the “2022 Acquired Remaining Equity”) at an implied CarOffer value (the “2022 Call Right Value”) of seven (7) times CarOffer’s trailing twelve months gross profit as of June 30, 2022 (calculated in accordance with the defined terms and subject to the adjustments set forth in the CarOffer Operating Agreement). If the 2022 Call Right is exercised by the Company, the 2022 Acquired Remaining Equity will be purchased ratably across all of the holders of CarOffer equity securities other than the Company. The consideration to be paid by the Company in connection with the exercise of the 2022 Call Right will be in the form of cash and/or shares of Class A common stock, as determined by the Company in its sole discretion. In the second half of 2024, (a) the Company will have a call right (the “2024 Call Right”), exercisable in its sole discretion, to acquire all, and not less than all, of the Remaining Equity that it has not acquired pursuant to the 2022 Call Right and the Closing, at the greater of (i) (x) one hundred million dollars ($ 100,000,000 ), and (y) the 2022 Call Right Value, whichever is less, and (ii) an implied CarOffer value of twelve (12) times CarOffer’s trailing twelve months EBITDA as of June 30, 2024 (in each case calculated in accordance with the defined terms and subject to the adjustments set forth in the CarOffer Operating Agreement), and (b) the representative of the holders of the Remaining Equity will have a put right (the “2024 Put Right”), exercisable in his, her or their sole discretion, to have the holders of the Remaining Equity sell to the Company, all, and not less than all, of the Remaining Equity at an implied CarOffer value of twelve (12) times CarOffer’s trailing twelve months EBITDA as of June 30, 2024 (calculated in accordance with the defined terms and subject to the adjustments set forth in the CarOffer Operating Agreement). The determination of whether the 2024 Call Right or the 2024 Put Right is ultimately exercised is as set forth in the CarOffer Operating Agreement. The consideration to be paid by the Company in connection with the exercise of either the 2024 Call Right or the 2024 Put Right, as applicable, will be in the form of cash and/or shares of Class A common stock, as determined by the Company in its sole discretion. The foregoing summary of the Purchase Agreement, the CarOffer Operating Agreement and the transactions contemplated thereby does not purport to be complete and is subject to, and qualified in its entirety by, the full text of the Purchase Agreement and the CarOffer Operating Agreement, which are filed as exhibits to the Annual Report. The following unaudited pro forma consolidated financial information combines the unaudited results of the Company for the three and nine months ended September 30, 2021 and 2020 and the unaudited results of CarOffer for the three and nine months ended September 30, 2021 and 2020, and assumes that the CarOffer Acquisition, which closed on January 14, 2021, was completed on January 1, 2020 (the first day of fiscal year 2020). The pro forma consolidated financial information has been calculated after applying the Company’s accounting policies and includes adjustments for amortization expense of acquired intangible assets, transaction-related costs, and compensation expense for ongoing share-based compensation arrangements replaced, together with the consequential tax effects. These pro forma results have been prepared for comparative purposes only and do not purport to be indicative of the operating results of the Company that would have been achieved had the CarOffer Acquisition actually taken place on January 1, 2020. In addition, these results are not intended to be a projection of future results and do not reflect events that may occur after September 30, 2021, including, but not limited to revenue enhancements, cost savings or operating synergies that the combined Company may achieve as a result of the CarOffer Acquisition. Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Revenue $ 222,915 $ 147,472 $ 614,970 $ 409,007 Consolidated net income (1) $ 29,267 $ 26,487 $ 75,897 $ 20,965 (1) For the three months ended September 30, 2021 , pro forma consolidated net income includes $ 7,286 and $ 1,083 related to intangibles amortization and stock-based compensation for CarOffer, respectively. For the three months ended September 30, 2020 , pro forma consolidated net income includes $ 7,275 and $ 1,083 related to intangibles amortization and stock-based compensation for CarOffer, respectively. For the nine months ended September 30, 2021 , pro forma consolidated net income includes $ 21,836 and $ 9,813 related to intangibles amortization and stock-based compensation for CarOffer, respectively. For the nine months ended September 30, 2020 , pro forma consolidated net income includes $ 21,825 and $ 9,628 related to intangibles amortization and stock-based compensation for CarOffer, respectively. $ 62,992 of revenue and $ 178 of net income attributable to CarOffer is included in our Unaudited Condensed Consolidated Income Statement for the three months ended September 30, 2021 . $ 135,847 of revenue and $ 8,912 of net loss attributable to CarOffer is included in our Unaudited Condensed Consolidated Income Statement from the Closing date of January 14, 2021 to September 30, 2021 .

Fair Value of Financial Instrum

Fair Value of Financial Instruments Including Cash, Cash Equivalents, and Investments	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments Including Cash, Cash Equivalents, and Investments	5. Fair Value of Financial Instruments Including Cash, Cash Equivalents, and Investments 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 September 30, 2021 and at December 31, 2020: At September 30, 2021 Quoted Prices Significant Other Significant Total Cash equivalents: Money market funds $ 167,521 $ — $ — $ 167,521 Investments: Certificates of deposit — 90,000 — 90,000 Total $ 167,521 $ 90,000 $ — $ 257,521 At December 31, 2020 Quoted Prices Significant Other Significant Total Cash equivalents: Money market funds $ 112,431 $ — $ — $ 112,431 Investments: Certificates of deposit — 100,000 — 100,000 Total $ 112,431 $ 100,000 $ — $ 212,431 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 as of September 30, 2021 and December 31, 2020. 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 and did not elect the fair value option for any financial assets transacted during the nine months ended September 30, 2021 or the year ended December 31, 2020. 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 considers all highly liquid investments with an original maturity of 90 days or less at the date of purchase to be cash equivalents. Investments not classified as cash equivalents with maturities one year or less 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. Certificates of deposit at September 30, 2021 and at December 31, 2020 had maturity dates of one year or less. The following is a summary of investments as of September 30, 2021 and December 31, 2020, respectively: At September 30, 2021 Amortized Gross Gross Estimated Investments: Certificates of deposit due in $ 90,000 $ — $ — $ 90,000 Total $ 90,000 $ — $ — $ 90,000 At December 31, 2020 Amortized Gross Gross Estimated Investments: Certificates of deposit due in $ 100,000 $ — $ — $ 100,000 Total $ 100,000 $ — $ — $ 100,000

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	6. Property and Equipment, Net Property and equipment, net consists of the following: At At Computer equipment $ 8,604 $ 8,108 Capitalized software 149 149 Capitalized website development 19,451 16,328 Furniture and fixtures 8,491 7,320 Leasehold improvements 24,086 20,507 Construction in progress 665 1,024 Finance lease right-of-use assets 610 41 62,056 53,477 Less accumulated depreciation and amortization ( 32,487 ) ( 25,994 ) Property and equipment, net $ 29,569 $ 27,483 Depreciation and amortization expense, excluding amortization of intangible assets and internal-use software, was $ 2,755 , $ 1,937 , $ 7,068 and $ 7,367 for the three months ended September 30, 2021 and 2020 and the nine months ended September 30, 2021 and 2020 , respectively. Amortization expense related to internal-use software was $ 47 and $ 61 for the three and nine months ended September 30, 2021 . There was no amortization expense related to internal-use software for the three and nine months ended September 30, 2020 .

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	9 Months Ended
	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	7. Goodwill and Other Intangible Assets Goodwill The changes in the carrying value of goodwill were as follows: Balance at December 31, 2020 $ 29,129 CarOffer acquisition (1) 127,500 Foreign currency translation adjustment ( 922 ) Balance at September 30, 2021 $ 155,707 (1) See Note 4 of the Unaudited Condensed Consolidated Financial Statements included elsewhere in this Quarterly Report. The Company tests goodwill for impairment at least annually or whenever events or changes in circumstances indicate that the carrying value may not be recoverable. As of September 30, 2021, there have been no events or changes in circumstance that indicate that the carrying value may not be recoverable. As of December 31, 2020, the Company assessed its goodwill for impairment and concluded that there was no impairment. Other Intangible Assets Intangible assets as of September 30, 2021 and December 31, 2020 consist of the following: At September 30, 2021 Weighted Gross Accumulated Net Carrying Brand 9.6 $ 32,338 $ 3,444 $ 28,894 Customer relationships 2.2 19,871 5,660 14,211 Developed technology 2.3 65,212 15,896 49,316 Total $ 117,421 $ 25,000 $ 92,421 At December 31, 2020 Weighted Gross Accumulated Net Carrying Brand 8.4 $ 9,405 $ 1,235 $ 8,170 Customer relationships 1.6 1,886 938 948 Developed technology 1.0 2,213 469 1,744 Total $ 13,504 $ 2,642 $ 10,862 The Company recorded amortization expense related to intangible assets of $ 7,854 , $ 495 , $ 22,358 , and $ 1,412 for the three months ended September 30, 2021 and 2020 and the nine months ended September 30, 2021 and 2020, respectively. The Company 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. As of September 30, 2021, there have been no events or changes in circumstances that could impact the recoverability of these assets. As of December 31, 2020, the Company assessed its intangible assets for impairment and concluded that there was no impairment . Estimated amortization expense of intangible assets for future periods as of September 30, 2021 is as follows: Year Ending December 31, Amortization Remainder of 2021 $ 7,874 2022 31,078 2023 30,350 2024 4,144 2025 3,052 2026 3,052 Thereafter 12,871 Total $ 92,421

Accrued Expenses, Accrued Incom

Accrued Expenses, Accrued Income Taxes and Other Current Liabilities	9 Months Ended
	Sep. 30, 2021
Accrued Liabilities and Other Liabilities [Abstract]
Accrued Expenses, Accrued Income Taxes and Other Current Liabilities	8. Accrued Expenses, Accrued Income Taxes and Other Current Liabilities Accrued expenses, accrued income taxes and other current liabilities consist of the following: At At Accrued bonus $ 7,372 $ 10,845 Accrued commissions 2,841 3,941 Other accrued expenses and other current liabilities 11,709 9,965 Total $ 21,922 $ 24,751 O

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	9. Commitments and Contingencies Contractual Obligations and Commitments All of the Company’s property, equipment, and internal-use software have been purchased with cash with the exception of amounts related to unpaid property and equipment and internal use software and amounts related to obligations under finance leases as disclosed in the Unaudited Condensed Consolidated Statements of Cash Flows as of September 30, 2021. The Company has no material long-term purchase obligations outstanding with any vendor or third party. Leases The Company’s primary operating lease obligations consist of various leases for office space in: Boston, Massachusetts; Cambridge, Massachusetts; San Francisco, California; Addison, Texas; Plano, Texas; and Dublin, Ireland. The Company also has an operating lease obligation for data center space in Needham, Massachusetts. As of September 30, 2021, there were no material changes in the Company’s leases from those disclosed in the Annual Report, other than as discussed below. On January 25, 2021, CarOffer entered into a sublease in Addison, Texas at 15601 Dallas Parkway for the lease of approximately 61,826 square feet of office space with a non-cancellable lease term through 2030 . The sublease commenced on March 1, 2021 . CarOffer’s monthly base rent for the premises, which is payable from January 1, 2022 , will initially be approximately $ 152 , and will increase each year up to a maximum monthly base rent of approximately $ 185 . In connection with the sublease, CarOffer entered into a financing lease arrangement for furniture and fixtures used in connection with its operations. The term of the financing lease is for the entire period of the sublease. The monthly rent for the furniture and fixtures is included in the sublease monthly rent, with ownership of the furniture and fixtures transferring to CarOffer at the expiration of the lease term. Monthly rent payments are allocated based upon the relative fair value of the office space and furniture of 95 % and 5 %, respectively. Upon commencement, the right of use asset for the office space and furniture was $ 12,336 and $ 664 , respectively. On July 1, 2019, CarOffer entered into a sublease in Plano, Texas at 2701 East Plano Parkway for the lease of approximately 26,971 square feet of office space with a non-cancellable lease term through 2023 . The sublease commenced on July 1, 2019 . CarOffer’s monthly base rent for the premises, which is payable from July 1, 2019 , was initially approximately $ 21 , and will increase each year up to maximum monthly base rent of $ 22 . The Company acquired the lease as part of the CarOffer Acquisition. The Company’s leases in Boston, Massachusetts, Cambridge, Massachusetts and San Francisco, California have associated letters of credit, which are recorded as restricted cash within the Unaudited Condensed Consolidated Balance Sheet. At September 30, 2021 and December 31, 2020, restricted cash was $ 16,130 and $ 10,627 , respectively, and primarily related to cash held at a financial institution in an interest‑bearing cash account as collateral for the letters of credit related to the contractual provisions for the Company’s building leases. Restricted cash at September 30, 2021 also includes pass-through payments from customers related to the Company’s wholesale business. At September 30, 2021 and December 31, 2020, portions of restricted cash were classified as a short-term asset and long‑term asset, as disclosed on the Unaudited Condensed Consolidated Balance Sheet. Acquisitions On January 14, 2021, the Company completed the CarOffer Acquisition, details of which are described in Note 4 of the Unaudited Condensed Consolidated Financial Statements included elsewhere in this Quarterly Report. 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, partners and service providers that include commercial provisions with respect to licensing, infringement, indemnification, and other common provisions. The Company does not, in the ordinary course, agree to guaranty or indemnification obligations for the Company under its contracts with customers. Based on historical experience and information known at September 30, 2021 and December 31, 2020 , the Company has not incurred any costs for guarantees or indemnities.

Stock-based Compensation

Stock-based Compensation	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Stock-based Compensation	10. Stock-based Compensation Equity Incentive Plans The 2020 CO Plan provides for the issuance of CO Incentive Units to CarOffer’s employees, officers, managers, and consultants. The 2020 CO Plan authorized up to an aggregate of 485,714 CO Incentive Units for such issuances. The Vesting Agreement provides for the vesting of the Subject Units beneficially owned by the T5 Holders, which vest in accordance with the terms described in Note 2 of the Unaudited Condensed Consolidated Financial Statements included elsewhere in this Quarterly Report. The 2021 CO Plan provides for an incentive equity grant structure whereby 2021 Incentive Units will be granted to CIE and 2021 CO Plan grantees will receive an associated CIE Interest, with back-to-back vesting between the 2021 Incentive Units and the associated CIE Interest. The 2021 CO Plan authorized up to an aggregate of 228,571 2021 Incentive Units for such issuances. Stock-based Compensation Expense The following two tables show stock compensation expense by award type and where the stock compensation expense is recorded in the Company’s Unaudited Condensed Consolidated Income Statements: Three Months Ended Nine Months Ended 2021 2020 2021 2020 Options $ 630 $ — $ 1,882 $ 17 Restricted stock units 13,852 11,030 41,539 34,617 CO Incentive Units and Subject 687 — 9,681 — Total stock-based $ 15,169 $ 11,030 $ 53,102 $ 34,634 Three Months Ended Nine Months Ended 2021 2020 2021 2020 Cost of revenue $ 110 $ 57 $ 311 $ 241 Sales and marketing expense 2,717 2,450 9,040 8,206 Product, technology, and 5,583 5,140 17,585 15,861 General and administrative expense 6,759 3,383 26,166 10,326 Total stock-based $ 15,169 $ 11,030 $ 53,102 $ 34,634 Excluded from stock-based compensation expense is $ 777 , $ 656 , $ 2,212 and $ 1,323 of capitalized website development and internal-use software costs for the three months ended September 30, 2021 and 2020 and the nine months ended September 30, 2021 and 2020, respectively. During the three months ended September 30, 2021 and 2020 and the nine months ended September 30, 2021 and 2020, the Company withheld 114,973 , 111,370 , 404,626 and 337,313 shares of Class A common stock, respectively, to satisfy employee tax withholding requirements and for option exercise costs due to net share settlements and cashless exercises of options. The shares withheld return to the authorized, but unissued pool under the 2017 Plan and can be reissued by the Company. Total payments to satisfy employee tax withholding requirements and for option exercise costs due to net share settlements and cashless exercises of options were $ 3,106 , $ 2,922 , $ 11,314 and $ 8,708 for the three months ended September 30, 2021 and 2020 and the nine months ended September 30, 2021 and 2020 , respectively, and are reflected as a financing activity within the Unaudited Condensed Consolidated Statements of Cash Flows.

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Earnings Per Share	11. Earnings Per Share 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 upon either the death or voluntary termination of the Company’s Executive Chairman. The Company allocates undistributed earnings attributable to common stock between the common stock classes on a one‑to‑one basis when computing net income per share. As a result, basic and diluted net income per share of Class A common stock and per share of Class B common stock are equivalent. During the three months ended September 30, 2021 and 2020, holders of Class B common stock converted 1,676,061 and 898,655 shares of Class B common stock to Class A common stock, respectively. During the nine months ended September 30, 2021 and 2020, holders of Class B common stock converted 2,605,658 and 1,238,144 shares of Class B common stock to Class A common stock, respectively. Basic net income per share (“Basic EPS”) is computed by dividing net income attributable to common stockholders and adjusted to reflect changes in the redemption value of the redeemable noncontrolling interest, if applicable, 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 plus the weighted-average of any additional shares issued and outstanding during the reporting period. Diluted net income per share (“Diluted EPS”) gives effect to all potentially dilutive securities. Diluted EPS is computed by dividing net income attributable to common stockholders and adjusted to reflect adjustments for net income (loss) attributable to the noncontrolling interest and redemption adjustments to redeemable noncontrolling interest , if applicable and dilutive, by the weighted-average number of common shares outstanding during the reporting period using (i) the number of shares of common stock used in the Basic EPS calculation as indicated above, (ii) if dilutive, the incremental weighted-average common stock that the Company would issue upon the exercise of stock options and the vesting of RSUs, (iii) if dilutive, market-based performance awards based on the number of shares that would be issuable as of the end of the reporting period assuming the end of the reporting period was also the end of the contingency period. The dilutive effect of these common stock equivalents is reflected in diluted earnings per share by application of the treasury stock method. The if-converted method is used to calculate the number of shares issuable upon exercise of the 2024 Put Right, inclusive of CarOffer noncontrolling interest and incentive units, that would be issuable as of the end of the reporting period assuming the end of the reporting period was also the end of the contingency period. The following table presents a reconciliation of the numerator and denominator used in the calculation of basic and diluted net income per share: Three Months Ended Nine Months Ended 2021 2020 2021 2020 Numerator: Consolidated net income $ 29,267 $ 32,563 $ 76,214 $ 52,390 Less: Net income (loss) attributable to 68 — ( 3,398 ) — Net income attributable to common $ 29,199 $ 32,563 $ 79,612 $ 52,390 Add: Net income (loss) attributable to 68 — ( 588 ) — Net income attributable to common $ 29,267 $ 32,563 $ 79,024 $ 52,390 Denominator: Weighted-average number of shares of 117,412,164 113,027,995 116,955,188 112,707,003 Dilutive effect of share equivalents 418,054 632,581 460,553 701,176 Dilutive effect of share equivalents 491,175 306,287 403,967 324,437 Dilutive effect of share equivalents 2,116,980 — 1,231,520 — Weighted-average number of shares 120,438,373 113,966,863 119,051,228 113,732,616 Net income per share attributable to Basic $ 0.25 $ 0.29 $ 0.68 $ 0.46 Diluted $ 0.24 $ 0.29 $ 0.66 $ 0.46 The following potentially dilutive common stock equivalents have been excluded from the calculation of diluted weighted-average shares outstanding for the three and nine months ended September 30, 2021 and 2020, as their effect would have been anti-dilutive for the periods presented: Three Months Ended Nine Months Ended 2021 2020 2021 2020 Stock options outstanding 588,490 — 501,306 — Restricted stock units outstanding 2,181,061 2,577,713 2,507,873 2,893,491 In addition, shares of Class A common stock potentially issuable under market-based performance awards of approximately 282,921 were excluded from the calculation of weighted average shares used to compute Diluted EPS for both the three and nine months ended September 30, 2021 as the market-based vesting conditions had not been achieved as of the reporting period end date and as such there were zero contingently issuable shares.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	12. Income Taxes During the three months ended September 30, 2021, the Company recorded an income tax provision of $ 10,952 , representing an effective tax rate of 27.3 % . The effective tax rate for the three months ended September 30, 2021 was higher than the statutory tax rate of 21 % principally due to state and local income taxes, shortfalls on the taxable compensation of share-based awards and the Section 162(m) excess officer compensation limitation, which became applicable in May 2021 upon the expiration of the transition period permitted following the Company’s initial public offering (“IPO”), partially offset by federal and state research and development tax credits. During the nine months ended September 30, 2021, the Company recorded an income tax provision of $ 28,556 , representing an effective tax rate of 26.4 % . The effective tax rate for the nine months ended September 30, 2021 was higher than the statutory tax rate of 21 % principally due to state and local income taxes, shortfalls on the taxable compensation of share-based awards and the Section 162(m) excess officer compensation limitation, which became applicable in May 2021 upon the expiration of the transition period permitted following the IPO, partially offset by federal and state research and development tax credits. During the three months ended September 30, 2020, the Company recorded an income tax provision of $ 11,209 , representing an effective tax rate of 25.6 %. The effective tax rate for the three months ended September 30, 2020 was higher than the statutory tax rate of 21 % principally due to state and local income taxes, partially offset by federal and state research and development tax credits. During the nine months ended September 30, 2020, the Company recorded an income tax provision of $ 13,312 , representing an effective tax rate of 20.3 %. The effective tax rate for the nine months ended September 30, 2020 was lower than the statutory tax rate of 21 % principally due to a discrete benefit recognized as a result of the enactment of the Coronavirus Aid, Relief, and Economic Security Act , excess stock deductions from the taxable compensation of stock-based awards and federal and state research and development tax credits, partially offset by state and local income taxes. The Company and its subsidiaries are subject to various U.S. federal, state, and foreign income tax examinations. The Company is currently not subject to income tax examination for the tax years of 2017 and prior as a result of applicable statute of limitations of the Internal Revenue Service (“IRS”) and state jurisdictions. The Company is currently open to examination in its foreign jurisdictions for tax years 2018 and after. In 2019, the IRS commenced a federal employment tax audit with respect to the 2018, 2017 and 2016 calendar years and expanded the audit to cover tax year 2019 as part of the audit settlement in July 2021. In 2020, the State of New York commenced a sales tax audit of the Company for the tax years 2014 to 2020 , which closed without adjustment.

Segment and Geographic Informat

Segment and Geographic Information	9 Months Ended
	Sep. 30, 2021
Segment Reporting [Abstract]
Segment and Geographic Information	13. 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 (the “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 and wholesale and other revenues from customers within the United States. The International segment derives revenues from marketplace subscriptions and other revenues from customers outside of the United States. A majority of the Company’s operational overhead expenses, including technology and personnel costs, and other general and administrative costs associated with running the Company’s business, are incurred in the United States and not allocated to the International segment. Revenue 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 as follows: Three Months Ended Nine Months Ended 2021 2020 2021 2020 Segment revenue: United States $ 211,554 $ 138,412 $ 581,149 $ 376,164 International 11,361 9,060 30,882 23,734 Total revenue $ 222,915 $ 147,472 $ 612,031 $ 399,898 Three Months Ended Nine Months Ended 2021 2020 2021 2020 Segment income (loss) from operations: United States $ 41,931 $ 46,462 $ 111,515 $ 82,061 International ( 1,855 ) ( 2,895 ) ( 7,171 ) ( 17,766 ) Total income from operations $ 40,076 $ 43,567 $ 104,344 $ 64,295 The Company ceased the operations of the International segment online marketplaces in Germany, Italy, and Spain in the second quarter of 2020. As of September 30, 2021, total assets held outside of the United States were $ 33,877 , primarily attributable to $ 15,728 of goodwill. As of December 31, 2020, total assets held outside of the United States were $ 32,012 , primarily attributable to $ 16,652 of goodwill.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying interim condensed consolidated financial statements (the “Unaudited Condensed Consolidated Financial Statements”) are unaudited. The Unaudited Condensed Consolidated Financial Statements and related disclosures 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 GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). The Unaudited Condensed Consolidated Financial Statements have also been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Accordingly, certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. The Unaudited Condensed Consolidated Financial Statements reflect all adjustments, consisting of only normal recurring adjustments, necessary for the fair presentation of the Company’s financial position as of September 30, 2021 and December 31, 2020, results of operations, comprehensive income, changes in shareholders’ equity for the three and nine months ended September 30, 2021 and 2020 and cash flows for the nine months ended September 30, 2021 and 2020. These interim period results are not necessarily indicative of the results to be expected for any other interim period or the full year. The Unaudited Condensed Consolidated Financial Statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020, filed with the SEC on February 12, 2021 (the “Annual Report”). While the Company disclosed other non-current liabilities separately in the Company's Quarterly Report on Form 10-Q for the quarter ended September 30, 2020, filed with the SEC on November 5, 2020, the accompanying Unaudited Condensed Consolidated Statements of Cash Flows for the nine months ended September 30, 2020 present other non-current liabilities with accrued expenses, accrued income taxes and other current liabilities to conform to the current year presentation, as other non-current liabilities did not meet the threshold for separate disclosure.
Principles of Consolidation	Principles of Consolidation The accompanying Unaudited Condensed Consolidated Financial Statements include the accounts of the Company and its subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Subsequent Event Considerations	Subsequent Event 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 for certain estimates or to identify matters that require additional disclosure. The Company has evaluated all subsequent events and determined that there are no material recognized or unrecognized subsequent events requiring disclosure.
Use of Estimates	Use of Estimates The preparation of the Unaudited Condensed Consolidated Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, and the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. Although the Company regularly assesses these estimates, actual results could differ materially from these estimates. 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. Changes in estimates are recorded in the period in which they become known. Significant estimates relied upon in preparing the Unaudited Condensed Consolidated Financial Statements include the determination of sales allowance and variable consideration in the Company’s revenue recognition, allowance for doubtful accounts, the valuation of a redeemable noncontrolling interest, the valuation of equity and liability-classified compensation awards under ASC 718, the expensing and capitalization of product, technology, and development costs for website development and internal‑use software, the valuation and recoverability of goodwill and intangible assets and other long-lived assets, and the recoverability of the Company’s net deferred tax assets and related valuation allowance. Accordingly, the Company considers these to be its critical accounting policies, and believes that of the Company’s significant accounting policies, these policies involve the greatest degree of judgment and complexity.
Concentration of Credit Risk	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, cash equivalents, and investments with multiple financial institutions, its deposits may often exceed governmental 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 three and nine months ended September 30, 2021 and 2020 , no individual customer accounted for more than 10% of total revenue. As of September 30, 2021 , two customers accounted for 30 % and 15 % of net accounts receivable, respectively. As of December 31, 2020 , one customer accounted for approximately 10 % of net accounts receivable. Included in net accounts receivable at September 30, 2021 and December 31, 2020 are $ 6,694 and $ 7,426 , respectively, of unbilled accounts receivable relating primarily to advertising customers billed in a period subsequent to services rendered.
Significant Accounting Policies	Significant Accounting Policies The Unaudited Condensed Consolidated Financial Statements reflect the application of certain significant accounting policies as described below and elsewhere in these notes to the Unaudited Condensed Consolidated Financial Statements. As of September 30, 2021 , the Company’s significant accounting policies and estimates, which are detailed in the Annual Report, have not changed, other than those impacted by the acquisition of a 51 % interest in CarOffer and recently issued equity awards, as described below.
Redeemable Noncontrolling Interest	Redeemable Noncontrolling Interest In connection with the Company’s acquisition of a 51 % interest in CarOffer on January 14, 2021, the Company became a party with the noncontrolling equity holders of CarOffer to the CarOffer Operating Agreement (as defined in Note 4 of the Unaudited Condensed Consolidated Financial Statements included elsewhere in this Quarterly Report), which, among other matters, sets forth certain put and call rights described in Note 4 of the Unaudited Condensed Consolidated Financial Statements included elsewhere in this Quarterly Report. The CarOffer Operating Agreement provides the Company with the right to purchase, and the noncontrolling equity holders with the right to sell to the Company, the noncontrolling CarOffer equity holders’ equity interests in CarOffer at a contractually defined formulaic purchase price, which is based on a multiple of earnings. As the purchase is contingently redeemable at the option of the noncontrolling equity holders, the Company classifies the carrying amount of the redeemable noncontrolling interests in the mezzanine section on the Unaudited Condensed Consolidated Balance Sheet, which is presented above the equity section and below the liabilities section. As of the date of Closing (as defined in Note 4 of the Unaudited Condensed Consolidated Financial Statements included elsewhere in this Quarterly Report), the noncontrolling interest was recognized at fair value computed using the Least Square Monte Carlo Simulation approach. Significant inputs to the model include market price of risk, volatility, correlation and risk-free rate. Subsequent to the Company’s acquisition of the 51 % interest on January 14, 2021, the redeemable noncontrolling interest is measured at the greater of the amount that would be paid if settlement occurred as of the balance sheet date based on the contractually defined redemption value and its carrying amount adjusted for net income (loss) attributable to the noncontrolling interest. Adjustments to the carrying value of the redeemable noncontrolling interest resulting from changes in the redemption value are recorded through retained earnings in the Unaudited Condensed Consolidated Balance Sheet.
Revenue Recognition - Wholesale and Other Revenue and Inventory	Revenue Recognition – Wholesale and Other Revenue and Inventory The Company generates wholesale and other revenue primarily from revenue relating to the wholesale sale of automobiles, display advertising revenue from auto manufacturers and other auto-related brand advertisers and revenue from partnerships with financing services companies. CarOffer revenue is comprised entirely of wholesale revenue. Wholesale revenue includes transaction fees earned by CarOffer from facilitating the purchase and sale of vehicles between dealers, where CarOffer collects fees from both the buyer and seller. CarOffer also sells vehicles to dealers that CarOffer acquires at other marketplaces or directly from consumers – in these instances, CarOffer collects a transaction fee from the buyer. CarOffer also charges the buyer fees to perform inspection and transportation services for all wholesale transactions. For facilitating the purchase and sale of vehicles between dealers, CarOffer generally does not control the vehicle and therefore acts as an agent in the transaction. Revenue earned from the fees for facilitating these transactions is recognized at a point in time when the vehicle is sold and revenue is recognized on a net basis. For vehicles sold to dealers that are acquired at other marketplaces, CarOffer generally does not control the vehicle and therefore acts as an agent in the transaction. Revenue earned from the fees for facilitating these transactions is recognized at a point in time when the vehicle is sold and revenue is typically recognized on a net basis. In these situations, the inventory is recorded on the balance sheet for the short period of time CarOffer possesses the vehicle title and is valued at the lower of cost or net realizable value. For vehicles sold to dealers that are acquired directly from consumers, CarOffer is deemed to control the vehicle and therefore is deemed to be the principal in the transaction. Revenue earned from the fees for facilitating these transactions is recognized point in time when the vehicle is sold and revenue is recognized on a gross basis. In these situations, the inventory is recorded on the balance sheet and is valued at the lower of cost or net realizable value. In certain circumstances, the vehicle may be arbitrated. For the majority of arbitrations, the vehicle is rematched to new buyers. In these situations, CarOffer is not deemed to control the vehicle and therefore is deemed to be an agent in the transaction. Revenue earned from the fees for facilitating these transactions is recognized at a point in time when the vehicle is sold and revenue is recognized on a net basis. In other limited situations, during an arbitration process, CarOffer acquires vehicles in transactions for which it is deemed to control the vehicle and therefore is deemed to be the principal in the transaction. Revenue earned from the fees for facilitating these transactions is recognized point in time and revenue is recognized on a gross basis. In these limited situations, the inventory is recorded on the balance sheet and is valued at the lower of cost or net realizable value. For inspection and transportation services, CarOffer leverages a network of third-party inspection service providers and transportation carriers. CarOffer is deemed to control both inspection and transportation services as it is primarily responsible for fulfillment and therefore acts as a principal in the transaction. Revenue from fees for inspection services is recognized at the point in time when the inspection is performed and revenue from fees for transportation services is recognized over time as delivery is completed. Revenue from both inspection and transportation services is recognized on a gross basis. Unearned revenue related to unsatisfied performance obligations is recorded as deferred revenue.
Stock-Based Compensation	Stock‑Based Compensation For stock‑based awards granted under the Company’s stock‑based compensation plans, the fair value of each award is determined on the date of grant. For restricted stock units (“RSUs”) granted subject to service-based vesting conditions, the fair value is determined based on the closing price of the Company’s Class A common stock , par value $ 0.001 per share (the “Class A common stock”), as reported on the Nasdaq Global Select Market on the date of grant. RSUs granted subject to service-based vesting conditions generally vest over a four-year requisite service period. For RSUs granted subject to market-based vesting conditions, the fair value is determined using the Monte Carlo simulation lattice model. The determination of the fair value using this model is affected by the Company’s stock price performance relative to the companies listed on the S&P 500 as of December 31, 2020 and a number of assumptions including volatility, correlation coefficient, risk-free interest rate and expected dividends. RSUs granted subject to market-based vesting conditions vest upon achievement of specified levels of market conditions . For stock options granted, the fair value is determined on the date of grant using the Black‑Scholes option‑pricing model. The determination of the fair value is affected by the Company’s stock price and a number of assumptions including volatility, term, risk-free interest rate and dividend yield. Stock options granted generally have a term of ten years from the date of grant and generally vest over a four-year requisite service period. In connection with the Company’s acquisition of a 51 % interest in CarOffer, the then-outstanding unvested incentive units (“CO Incentive Units”) of CarOffer and unvested Class CO CarOffer units (“the Subject Units”) remained outstanding and will vest over the requisite service periods as discussed below. Grants of the CO Incentive Units are subject to the CarOffer 2020 Equity Incentive Plan, adopted effective November 24, 2020 (the “2020 CO Plan”) , the applicable award agreement, and the CarOffer Operating Agreement . Following the Company’s acquisition of the 51 % interest in CarOffer on January 14, 2021, remaining unvested incentive interests will vest over a period of three ( 3 ) years, one third each on the first, second, and third anniversaries of January 14, 2021, provided that a grantee’s continuous service to CarOffer has not terminated on the applicable vesting date. Under the terms of the grants, vesting of unvested incentive interests is accelerated in the event of (i) a change of control of CarOffer (which, for the avoidance of doubt, does not include the Company’s acquisition of the 51 % interest on January 14, 2021), (ii) the death or disability of the grantee, (iii) termination of the grantee’s employment with CarOffer without cause, or (iv) termination of grantee’s employment by the grantee for good reason. Upon termination of a grantee’s continuous service to CarOffer voluntarily by the grantee (other than for good reason) or by CarOffer for cause, all of such grantee’s unvested incentive interests are forfeited. In addition, if a grantee’s continuous service terminates, then CarOffer has the option to repurchase any outstanding incentive interests from the grantee. In addition to the 2020 CO Plan, on December 9, 2020 CarOffer entered into a Vesting Agreement (the “Vesting Agreement”) regarding the vesting of CarOffer equity interests beneficially owned by Bruce Thompson, the founder and CEO of CarOffer, and certain affiliated persons (the “T5 Holders”) in connection with the Company’s then-anticipated acquisition of a 51 % interest in CarOffer. Pursuant to the Vesting Agreement, 432,592 Subject Units beneficially owned by the T5 Holders will vest in three (3) equal installments on the first, second, and third anniversary of the closing of the CarOffer Acquisition. As more particularly described in the Vesting Agreement, unvested Subject Units are subject to forfeiture in the event that Mr. Thompson’s relationship with CarOffer terminates other than in the event of a termination without cause (as defined in the Vesting Agreement) or due to Mr. Thompson’s death or disability. The Vesting Agreement also provides for acceleration of any unvested Subject Units in the event of the termination of Mr. Thompson’s employment with CarOffer without cause, Mr. Thompson’s death or disability, or the consummation of an eligible liquidity event (as defined in the Vesting Agreement). In connection with the Closing of the Company’s acquisition of the 51 % interest in CarOffer , CarOffer reserved 228,571 incentive units (the "2021 Incentive Units") for purposes of establishing an employee incentive equity plan. Thereafter, CarOffer formed CarOffer Incentive Equity, LLC (“CIE”), a Delaware manager-managed limited liability company managed by the Company, and established the CIE 2021 Equity Incentive Plan (the “2021 CO Plan). The 2021 CO Plan and related documentation, including the applicable award agreement, a vesting agreement between CarOffer and CIE, and the CarOffer Operating Agreement, provide for an incentive equity grant structure whereby 2021 Incentive Units will be granted to CIE and 2021 CO Plan grantees will receive an associated equity interest in CIE (the “CIE Interest”), with back-to-back vesting between the 2021 Incentive Units and the associated CIE Interest. Subject to any modifications as may be approved by the CarOffer Board of Managers in its discretion, grants under the 2021 CO Plan will vest over a period of three ( 3 ) years from the grant date, one third each on the first, second, and third anniversaries of the applicable grant date, provided that a grantee’s continuous service to CarOffer has not terminated on the applicable grant date. Upon termination of a grantee’s continuous service to CarOffer, all of such grantee’s unvested 2021 Incentive Units are forfeited. As of September 30, 2021 there had not been any grants of 2021 Incentive Units under the 2021 CO Plan. CO Incentive Units, Subject Units and 2021 Incentive Units are liability-classified awards because the awards can be put to the Company at a formula price such that the holders do not bear the risks and rewards associated with equity ownership . For liability-classified awards, the fair value is determined on the date of issuance using a Least Square Monte Carlo simulation model. The determination of the fair value is affected by CarOffer’s equity value, EBITDA, Excess Parent Capital (as defined in the CarOffer Operating Agreement), and revenue forecasts that drive the exercise price of future call/put rights, as well as a number of assumptions including market price of risk, volatility, correlation, and risk-free interest rate. Liability-classified awards are remeasured to fair value each period until settlement. The Company issues shares for RSUs and stock option exercises out of its shares available for issuance. The Company issues CO Incentive Units out of CarOffer’s units available for issuance. The Company accounts for forfeitures when they occur. The Company recognizes compensation expense 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. The tax effect of differences between tax deductions related to stock compensation and the corresponding financial statement expense compensation are recorded to tax expense. Excess tax benefits recognized on stock‑based compensation expense are classified as an operating activity in the Unaudited Condensed Consolidated Statements of Cash Flows.
Recent Accounting Pronouncements Adopted	Recent Accounting Pronouncements Adopted Income Taxes In December 2019, the FASB issued ASU 2019-12, Income Taxes – Simplifying the Accounting for Income Taxes (“ASU 2019-12”). ASU 2019-12 simplifies the accounting for income taxes by removing several exceptions in the current standard and adding guidance to reduce complexity in certain areas, such as requiring that an entity reflect the effect of an enacted change in tax laws or rates in the annual effective tax rate computation in the interim period that includes the enactment date. The standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020, with early adoption permitted. The Company adopted the guidance on January 1, 2021 . The adoption did no t have an impact on the Unaudited Condensed Consolidated Financial Statements.
Recent Accounting Pronouncements not Yet Adopted	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. As of September 30, 2021, there are no new accounting pronouncements that the Company is considering adopting.
Fair Value of Financial Instruments Including Cash, Cash Equivalents, and Investments	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 as of September 30, 2021 and December 31, 2020. 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 and did not elect the fair value option for any financial assets transacted during the nine months ended September 30, 2021 or the year ended December 31, 2020. 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 considers all highly liquid investments with an original maturity of 90 days or less at the date of purchase to be cash equivalents. Investments not classified as cash equivalents with maturities one year or less 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. Certificates of deposit at September 30, 2021 and at December 31, 2020 had maturity dates of one year or less.
Goodwill and Other Intangible Assets	As of December 31, 2020, the Company assessed its goodwill for impairment and concluded that there was no impairment. As of December 31, 2020, the Company assessed its intangible assets for impairment and concluded that there was no impairment .
Earnings Per Share	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 upon either the death or voluntary termination of the Company’s Executive Chairman. The Company allocates undistributed earnings attributable to common stock between the common stock classes on a one‑to‑one basis when computing net income per share. As a result, basic and diluted net income per share of Class A common stock and per share of Class B common stock are equivalent.
Income Taxes	The Company and its subsidiaries are subject to various U.S. federal, state, and foreign income tax examinations. The Company is currently not subject to income tax examination for the tax years of 2017 and prior as a result of applicable statute of limitations of the Internal Revenue Service (“IRS”) and state jurisdictions. The Company is currently open to examination in its foreign jurisdictions for tax years 2018 and after. In 2019, the IRS commenced a federal employment tax audit with respect to the 2018, 2017 and 2016 calendar years and expanded the audit to cover tax year 2019 as part of the audit settlement in July 2021. In 2020, the State of New York commenced a sales tax audit of the Company for the tax years 2014 to 2020 , which closed without adjustment.

Revenue Recognition (Tables)

Revenue Recognition (Tables)	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Summary of Revenue from Contracts with Customers by Geographical Region and by Revenue	The following table summarizes revenue from contracts with customers by geographical region and by revenue source for the three and nine months ended September 30, 2021 and 2020. Three Months Ended Nine Months Ended 2021 2020 2021 2020 United States Marketplace subscription revenue $ 134,261 $ 121,814 $ 400,377 $ 330,295 Wholesale and other revenue 77,293 16,598 180,772 45,869 Total 211,554 138,412 581,149 376,164 International Marketplace subscription revenue 10,328 8,139 28,017 21,477 Wholesale and other revenue 1,033 921 2,865 2,257 Total 11,361 9,060 30,882 23,734 Total Revenue Marketplace subscription revenue 144,589 129,953 428,394 351,772 Wholesale and other revenue 78,326 17,519 183,637 48,126 Total $ 222,915 $ 147,472 $ 612,031 $ 399,898

Acquisitions (Tables)

Acquisitions (Tables)	9 Months Ended
	Sep. 30, 2021
Business Combinations [Abstract]
Summary of Total Consideration Transferred	The following table presents the total consideration transferred. Consideration Transferred Cash paid, net of cash acquired $ 64,273 Cash acquired 5,237 Cash consideration 69,510 Stock consideration 103,645 Total consideration transferred $ 173,155
Summary of Preliminary Purchase Price Allocation	The Company’s 51 % interest in CarOffer represents a controlling financial interest in the entity as the minority interest holders only have protective rights such that CarOffer is consolidated as of the date of Closing. The following table presents the preliminary purchase price allocation recorded in the Company’s Unaudited Condensed Consolidated Balance Sheet as of the date of Closing, which is subject to finalization for estimates of the fair value of assets acquired and liabilities assumed as of the date of Closing, including, but not limited to tangible assets, intangible assets and tax-related items, and the related tax effects of any changes made: Adjusted Fair Cash and cash equivalents $ 5,237 Accounts receivable 16,119 Inventory 2,338 Prepaid expenses, prepaid income taxes and other current assets 95 Property and equipment, net 198 Intangible assets (1) 104,100 Goodwill (2) 127,500 Operating lease right-of-use assets 709 Accounts payable ( 8,888 ) Accrued expenses, accrued income taxes, and other current liabilities ( 15,513 ) Operating lease liabilities - current ( 230 ) Operating lease liabilities - non-current ( 479 ) Redeemable noncontrolling interest (3) ( 58,031 ) Total consideration transferred $ 173,155 (1) Identifiable definite-lived intangible assets were comprised of developed technology, brand, and customer relationships of $ 63,000 , $ 23,100 , and $ 18,000 , respectively, with estimated useful lives of 3 years, 11 years, and 3 years, respectively, which will be amortized on a straight-line basis over their estimated useful lives. The fair value of the developed technology has been estimated using the multi-period excess earnings method which is a variation of the income approach. The fair value of the brand and customer relationships has been estimated using the relief from royalty method and the with/without approach, respectively. (2) Goodwill represents the excess value of the purchase price over net assets acquired, primarily attributable to adding wholesale vehicle acquisition and selling capabilities to CarGurus’ portfolio of dealer offerings. All goodwill is assigned to the United States reporting segment. For tax purposes, $ 28,991 of the goodwill is deductible under IRC Section 197 upon finalization of the transaction cost study. In connection with the transaction, the Company accelerated certain stock options deemed to be outside of consideration transferred. Therefore, the Company recognized an additional $ 1,229 of stock-based compensation expense during the nine months ended September 30, 2021. (3) The fair value of the redeemable noncontrolling interest has been estimated using the Least Square Monte Carlo Simulation approach. Significant inputs include market price of risk, volatility, correlation and risk-free rate.
Unaudited Pro Forma Consolidated Financial Information	The following unaudited pro forma consolidated financial information combines the unaudited results of the Company for the three and nine months ended September 30, 2021 and 2020 and the unaudited results of CarOffer for the three and nine months ended September 30, 2021 and 2020, and assumes that the CarOffer Acquisition, which closed on January 14, 2021, was completed on January 1, 2020 (the first day of fiscal year 2020). The pro forma consolidated financial information has been calculated after applying the Company’s accounting policies and includes adjustments for amortization expense of acquired intangible assets, transaction-related costs, and compensation expense for ongoing share-based compensation arrangements replaced, together with the consequential tax effects. These pro forma results have been prepared for comparative purposes only and do not purport to be indicative of the operating results of the Company that would have been achieved had the CarOffer Acquisition actually taken place on January 1, 2020. In addition, these results are not intended to be a projection of future results and do not reflect events that may occur after September 30, 2021, including, but not limited to revenue enhancements, cost savings or operating synergies that the combined Company may achieve as a result of the CarOffer Acquisition. Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Revenue $ 222,915 $ 147,472 $ 614,970 $ 409,007 Consolidated net income (1) $ 29,267 $ 26,487 $ 75,897 $ 20,965 (1) For the three months ended September 30, 2021 , pro forma consolidated net income includes $ 7,286 and $ 1,083 related to intangibles amortization and stock-based compensation for CarOffer, respectively. For the three months ended September 30, 2020 , pro forma consolidated net income includes $ 7,275 and $ 1,083 related to intangibles amortization and stock-based compensation for CarOffer, respectively. For the nine months ended September 30, 2021 , pro forma consolidated net income includes $ 21,836 and $ 9,813 related to intangibles amortization and stock-based compensation for CarOffer, respectively. For the nine months ended September 30, 2020 , pro forma consolidated net income includes $ 21,825 and $ 9,628 related to intangibles amortization and stock-based compensation for CarOffer, respectively.

Fair Value of Financial Instr_2

Fair Value of Financial Instruments Including Cash, Cash Equivalents, and Investments (Tables)	9 Months Ended
	Sep. 30, 2021
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 September 30, 2021 and at December 31, 2020: At September 30, 2021 Quoted Prices Significant Other Significant Total Cash equivalents: Money market funds $ 167,521 $ — $ — $ 167,521 Investments: Certificates of deposit — 90,000 — 90,000 Total $ 167,521 $ 90,000 $ — $ 257,521 At December 31, 2020 Quoted Prices Significant Other Significant Total Cash equivalents: Money market funds $ 112,431 $ — $ — $ 112,431 Investments: Certificates of deposit — 100,000 — 100,000 Total $ 112,431 $ 100,000 $ — $ 212,431
Schedule of Investments	The following is a summary of investments as of September 30, 2021 and December 31, 2020, respectively: At September 30, 2021 Amortized Gross Gross Estimated Investments: Certificates of deposit due in $ 90,000 $ — $ — $ 90,000 Total $ 90,000 $ — $ — $ 90,000 At December 31, 2020 Amortized Gross Gross Estimated Investments: Certificates of deposit due in $ 100,000 $ — $ — $ 100,000 Total $ 100,000 $ — $ — $ 100,000

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consists of the following: At At Computer equipment $ 8,604 $ 8,108 Capitalized software 149 149 Capitalized website development 19,451 16,328 Furniture and fixtures 8,491 7,320 Leasehold improvements 24,086 20,507 Construction in progress 665 1,024 Finance lease right-of-use assets 610 41 62,056 53,477 Less accumulated depreciation and amortization ( 32,487 ) ( 25,994 ) Property and equipment, net $ 29,569 $ 27,483

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	9 Months Ended
	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Summary of Changes in Carrying Value of Goodwill	The changes in the carrying value of goodwill were as follows: Balance at December 31, 2020 $ 29,129 CarOffer acquisition (1) 127,500 Foreign currency translation adjustment ( 922 ) Balance at September 30, 2021 $ 155,707 (1) See Note 4 of the Unaudited Condensed Consolidated Financial Statements included elsewhere in this Quarterly Report.
Summary of Other Intangible Assets	Intangible assets as of September 30, 2021 and December 31, 2020 consist of the following: At September 30, 2021 Weighted Gross Accumulated Net Carrying Brand 9.6 $ 32,338 $ 3,444 $ 28,894 Customer relationships 2.2 19,871 5,660 14,211 Developed technology 2.3 65,212 15,896 49,316 Total $ 117,421 $ 25,000 $ 92,421 At December 31, 2020 Weighted Gross Accumulated Net Carrying Brand 8.4 $ 9,405 $ 1,235 $ 8,170 Customer relationships 1.6 1,886 938 948 Developed technology 1.0 2,213 469 1,744 Total $ 13,504 $ 2,642 $ 10,862
Summary of Estimated Amortization Expense of Intangible Assets	Estimated amortization expense of intangible assets for future periods as of September 30, 2021 is as follows: Year Ending December 31, Amortization Remainder of 2021 $ 7,874 2022 31,078 2023 30,350 2024 4,144 2025 3,052 2026 3,052 Thereafter 12,871 Total $ 92,421

Accrued Expenses, Accrued Inc_2

Accrued Expenses, Accrued Income Taxes and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Accrued Liabilities and Other Liabilities [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 At Accrued bonus $ 7,372 $ 10,845 Accrued commissions 2,841 3,941 Other accrued expenses and other current liabilities 11,709 9,965 Total $ 21,922 $ 24,751 O

Stock-based Compensation (Table

Stock-based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Summary of Stock-based Compensation Expense by Award Type	The following two tables show stock compensation expense by award type and where the stock compensation expense is recorded in the Company’s Unaudited Condensed Consolidated Income Statements: Three Months Ended Nine Months Ended 2021 2020 2021 2020 Options $ 630 $ — $ 1,882 $ 17 Restricted stock units 13,852 11,030 41,539 34,617 CO Incentive Units and Subject 687 — 9,681 — Total stock-based $ 15,169 $ 11,030 $ 53,102 $ 34,634
Summary of Allocation of Stock-based Compensation Expense	Three Months Ended Nine Months Ended 2021 2020 2021 2020 Cost of revenue $ 110 $ 57 $ 311 $ 241 Sales and marketing expense 2,717 2,450 9,040 8,206 Product, technology, and 5,583 5,140 17,585 15,861 General and administrative expense 6,759 3,383 26,166 10,326 Total stock-based $ 15,169 $ 11,030 $ 53,102 $ 34,634

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of Reconciliation of Numerator and Denominator Used in Calculation of Basic and Diluted Net Income Per Share	The following table presents a reconciliation of the numerator and denominator used in the calculation of basic and diluted net income per share: Three Months Ended Nine Months Ended 2021 2020 2021 2020 Numerator: Consolidated net income $ 29,267 $ 32,563 $ 76,214 $ 52,390 Less: Net income (loss) attributable to 68 — ( 3,398 ) — Net income attributable to common $ 29,199 $ 32,563 $ 79,612 $ 52,390 Add: Net income (loss) attributable to 68 — ( 588 ) — Net income attributable to common $ 29,267 $ 32,563 $ 79,024 $ 52,390 Denominator: Weighted-average number of shares of 117,412,164 113,027,995 116,955,188 112,707,003 Dilutive effect of share equivalents 418,054 632,581 460,553 701,176 Dilutive effect of share equivalents 491,175 306,287 403,967 324,437 Dilutive effect of share equivalents 2,116,980 — 1,231,520 — Weighted-average number of shares 120,438,373 113,966,863 119,051,228 113,732,616 Net income per share attributable to Basic $ 0.25 $ 0.29 $ 0.68 $ 0.46 Diluted $ 0.24 $ 0.29 $ 0.66 $ 0.46
Schedule of Potentially Dilutive Common Stock Equivalents Excluded from Calculation of Diluted Weighted-average Shares Outstanding	The following potentially dilutive common stock equivalents have been excluded from the calculation of diluted weighted-average shares outstanding for the three and nine months ended September 30, 2021 and 2020, as their effect would have been anti-dilutive for the periods presented: Three Months Ended Nine Months Ended 2021 2020 2021 2020 Stock options outstanding 588,490 — 501,306 — Restricted stock units outstanding 2,181,061 2,577,713 2,507,873 2,893,491

Segment and Geographic Inform_2

Segment and Geographic Information (Tables)	9 Months Ended
	Sep. 30, 2021
Segment Reporting [Abstract]
Summary of Operations by Segment and Geographical Area	Information regarding the Company’s operations by segment and geographical area is presented as follows: Three Months Ended Nine Months Ended 2021 2020 2021 2020 Segment revenue: United States $ 211,554 $ 138,412 $ 581,149 $ 376,164 International 11,361 9,060 30,882 23,734 Total revenue $ 222,915 $ 147,472 $ 612,031 $ 399,898 Three Months Ended Nine Months Ended 2021 2020 2021 2020 Segment income (loss) from operations: United States $ 41,931 $ 46,462 $ 111,515 $ 82,061 International ( 1,855 ) ( 2,895 ) ( 7,171 ) ( 17,766 ) Total income from operations $ 40,076 $ 43,567 $ 104,344 $ 64,295

Organization and Business Des_2

Organization and Business Description - Additional Information (Details) - Segment	9 Months Ended
	Sep. 30, 2021	Mar. 31, 2021	Jan. 14, 2021
Business Acquisition [Line Items]
State of incorporation	DE
Date of incorporation	Jun. 26, 2015
Number of reportable segments	2
Car Offer
Business Acquisition [Line Items]
Business acquisition, percentage of interest acquired	51.00%	51.00%	51.00%

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details) $ / shares in Units, $ in Thousands	Dec. 09, 2020Installmentshares	Sep. 30, 2021USD ($)Customer$ / sharesshares	Sep. 30, 2020Customer	Sep. 30, 2021USD ($)Customer$ / sharesshares	Sep. 30, 2020Customer	Dec. 31, 2020USD ($)Customer$ / shares	Mar. 31, 2021	Jan. 14, 2021
Summary Of Significant Accounting Policies [Line Items]
Description of significant off-balance sheet risk				The Company has no significant off‑balance sheet risk, such as foreign exchange contracts, option contracts, or other foreign hedging arrangements.
ASU 2019-12
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted		true		true
Change in accounting principle, accounting standards update, adoption date		Jan. 1, 2021		Jan. 1, 2021
Change in accounting principle, accounting standards update, immaterial effect		true		true
Change in accounting principle, accounting standards update, transition option elected				ASU 2019-12
2020 CO Plan
Summary Of Significant Accounting Policies [Line Items]
Requisite service period				3 years
Number of shares authorized for issuances | shares		485,714		485,714
2021 CO Plan
Summary Of Significant Accounting Policies [Line Items]
Requisite service period				3 years
Number of shares authorized for issuances | shares		228,571		228,571
Class A Common Stock
Summary Of Significant Accounting Policies [Line Items]
Common stock, par value | $ / shares		$ 0.001		$ 0.001		$ 0.001
Car Offer
Summary Of Significant Accounting Policies [Line Items]
Business acquisition, percentage of interest acquired		51.00%		51.00%			51.00%	51.00%
Car Offer | Vesting Agreement
Summary Of Significant Accounting Policies [Line Items]
Business acquisition, percentage of interest acquired	51.00%
Vesting number of shares | shares	432,592
Number of Installment | Installment	3
Car Offer | Restricted Stock Units
Summary Of Significant Accounting Policies [Line Items]
Requisite service period				4 years
Car Offer | Stock Options
Summary Of Significant Accounting Policies [Line Items]
Requisite service period				4 years
Vesting period				10 years
Car Offer | Class A Common Stock
Summary Of Significant Accounting Policies [Line Items]
Common stock, par value | $ / shares		$ 0.001		$ 0.001
Sales Revenue, Net | Concentration of Credit Risk
Summary Of Significant Accounting Policies [Line Items]
Number of major customers | Customer		0	0	0	0
Net Accounts Receivable | Advertising Customers
Summary Of Significant Accounting Policies [Line Items]
Unbilled accounts receivable | $		$ 6,694		$ 6,694		$ 7,426
Net Accounts Receivable | Concentration of Credit Risk | Customer One
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk, percentage				30.00%		10.00%
Number of major customers | Customer						1
Net Accounts Receivable | Concentration of Credit Risk | Customer Two
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk, percentage				15.00%
Number of major customers | Customer				2

Revenue Recognition - Summary o

Revenue Recognition - Summary of Revenue from Contracts with Customers by Geographical Region and by Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation Of Revenue [Line Items]
Revenue	$ 222,915	$ 147,472	$ 612,031	$ 399,898
Marketplace Subscription Revenue
Disaggregation Of Revenue [Line Items]
Revenue	144,589	129,953	428,394	351,772
Wholesale and Other Revenue
Disaggregation Of Revenue [Line Items]
Revenue	78,326	17,519	183,637	48,126
United States
Disaggregation Of Revenue [Line Items]
Revenue	211,554	138,412	581,149	376,164
United States | Marketplace Subscription Revenue
Disaggregation Of Revenue [Line Items]
Revenue	134,261	121,814	400,377	330,295
United States | Wholesale and Other Revenue
Disaggregation Of Revenue [Line Items]
Revenue	77,293	16,598	180,772	45,869
International
Disaggregation Of Revenue [Line Items]
Revenue	11,361	9,060	30,882	23,734
International | Marketplace Subscription Revenue
Disaggregation Of Revenue [Line Items]
Revenue	10,328	8,139	28,017	21,477
International | Wholesale and Other Revenue
Disaggregation Of Revenue [Line Items]
Revenue	$ 1,033	$ 921	$ 2,865	$ 2,257

Revenue Recognition - Additiona

Revenue Recognition - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	2 Months Ended	3 Months Ended		9 Months Ended
	Jun. 30, 2020	May 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation Of Revenue [Line Items]
Performance obligation unsatisfied			$ 12,200		$ 12,200
Revenue recognized			$ 13,120	$ 8,195	$ 9,137	$ 9,984
All Marketplace Subscriptions
Disaggregation Of Revenue [Line Items]
Percentage fee reduction on marketplace subscription services		50.00%
United States
Disaggregation Of Revenue [Line Items]
Percentage fee reduction on marketplace subscription services	20.00%
Canada
Disaggregation Of Revenue [Line Items]
Percentage fee reduction on marketplace subscription services	20.00%
United Kingdom
Disaggregation Of Revenue [Line Items]
Percentage fee reduction on marketplace subscription services	50.00%

Acquisitions - Additional Infor

Acquisitions - Additional Information (Details) - USD ($)	Jan. 14, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2024	Dec. 31, 2022
Business Acquisition [Line Items]
Issuance of stock for acquisition								$ 103,645,000
Revenue		$ 222,915,000			$ 147,472,000			612,031,000	$ 399,898,000
Net income (loss)		$ 29,199,000	$ 28,052,000	$ 22,361,000	$ 32,563,000	$ 7,131,000	$ 12,696,000	$ 79,612,000	$ 52,390,000
Car Offer
Business Acquisition [Line Items]
Business acquisition date	Jan. 14, 2021
Business acquisition, percentage of interest acquired	51.00%	51.00%		51.00%				51.00%
Business acquisition, total consideration	$ 173,155,000
Issuance of stock for acquisition	103,645,000
Payments to acquire business	69,510,000
Retention pool aggregate amount	8,000,000
Retention pool amount granted to employees	6,000,000
Retention pool amount available for issuance to future employees	2,000,000
Acquisition-related costs incurred		$ 2,647,000						$ 2,647,000
Revenue		62,992,000						135,847,000
Net income (loss)		178,000						(8,912,000)
Car Offer | 2022 Call Right | Forecast
Business Acquisition [Line Items]
Business acquisition, option to acquire remaining percentage of interest											25.00%
Business acquisition, option to acquire remaining value of interest										$ 100,000,000
Car Offer | General and Administrative
Business Acquisition [Line Items]
Acquisition-related costs incurred		$ 0						$ 709,000
Car Offer | Class A Common Stock
Business Acquisition [Line Items]
Issuance of stock for acquisition	$ 103,645,000
Business acquisition, stock consideration shares issued	3,115,282
Business acquisition, share price	$ 22.51

Acquisitions - Summary of Total

Acquisitions - Summary of Total Consideration Transferred (Details) - USD ($) $ in Thousands	Jan. 14, 2021	Sep. 30, 2021	Sep. 30, 2020
Business Acquisition [Line Items]
Cash paid, net of cash acquired		$ 64,273	$ 21,056
Stock consideration		$ 103,645
Car Offer
Business Acquisition [Line Items]
Cash paid, net of cash acquired	$ 64,273
Cash acquired	5,237
Cash consideration	69,510
Stock consideration	103,645
Total consideration transferred	$ 173,155

Acquisitions - Summary of Preli

Acquisitions - Summary of Preliminary Purchase Price Allocation (Details) - USD ($) $ in Thousands		Sep. 30, 2021	Jan. 14, 2021	Dec. 31, 2020
Business Acquisition [Line Items]
Goodwill		$ 155,707		$ 29,129
Car Offer
Business Acquisition [Line Items]
Cash and cash equivalents			$ 5,237
Accounts receivable			16,119
Inventory			2,338
Prepaid expenses, prepaid income taxes and other current assets			95
Property and equipment, net			198
Intangible assets	[1]		104,100
Goodwill	[2]		127,500
Operating lease right-of-use assets			709
Accounts payable			(8,888)
Accrued expenses, accrued income taxes, and other current liabilities			(15,513)
Operating lease liabilities - current			(230)
Operating lease liabilities - non-current			(479)
Redeemable noncontrolling interest	[3]		(58,031)
Total consideration transferred			$ 173,155
[1]	Identifiable definite-lived intangible assets were comprised of developed technology, brand, and customer relationships of $ 63,000 , $ 23,100 , and $ 18,000 , respectively, with estimated useful lives of 3 years, 11 years, and 3 years, respectively, which will be amortized on a straight-line basis over their estimated useful lives. The fair value of the developed technology has been estimated using the multi-period excess earnings method which is a variation of the income approach. The fair value of the brand and customer relationships has been estimated using the relief from royalty method and the with/without approach, respectively.
[2]	Goodwill represents the excess value of the purchase price over net assets acquired, primarily attributable to adding wholesale vehicle acquisition and selling capabilities to CarGurus’ portfolio of dealer offerings. All goodwill is assigned to the United States reporting segment. For tax purposes, $ 28,991 of the goodwill is deductible under IRC Section 197 upon finalization of the transaction cost study. In connection with the transaction, the Company accelerated certain stock options deemed to be outside of consideration transferred. Therefore, the Company recognized an additional $ 1,229 of stock-based compensation expense during the nine months ended September 30, 2021.
[3]	The fair value of the redeemable noncontrolling interest has been estimated using the Least Square Monte Carlo Simulation approach. Significant inputs include market price of risk, volatility, correlation and risk-free rate.

Acquisitions - Summary of Pre_2

Acquisitions - Summary of Preliminary Purchase Price Allocation (Parenthetical) (Details) - Car Offer - USD ($) $ in Thousands		Jan. 14, 2021	Sep. 30, 2021
Business Acquisition [Line Items]
Intangible assets	[1]	$ 104,100
Goodwill estimated to be deductible under IRC Section 197		28,991
Additional stock-based compensation expense			$ 1,229
Developed Technology
Business Acquisition [Line Items]
Intangible assets		$ 63,000
Estimated useful lives		3 years
Brand
Business Acquisition [Line Items]
Intangible assets		$ 23,100
Estimated useful lives		11 years
Customer Relationships
Business Acquisition [Line Items]
Intangible assets		$ 18,000
Estimated useful lives		3 years
[1]	Identifiable definite-lived intangible assets were comprised of developed technology, brand, and customer relationships of $ 63,000 , $ 23,100 , and $ 18,000 , respectively, with estimated useful lives of 3 years, 11 years, and 3 years, respectively, which will be amortized on a straight-line basis over their estimated useful lives. The fair value of the developed technology has been estimated using the multi-period excess earnings method which is a variation of the income approach. The fair value of the brand and customer relationships has been estimated using the relief from royalty method and the with/without approach, respectively.

Acquisitions - Unaudited Pro Fo

Acquisitions - Unaudited Pro Forma Consolidated Financial Information (Details) - Car Offer - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Business Acquisition [Line Items]
Revenue	$ 222,915	$ 147,472	$ 614,970	$ 409,007
Consolidated net income	$ 29,267	$ 26,487	$ 75,897	$ 20,965

Acquisitions - Unaudited Pro _2

Acquisitions - Unaudited Pro Forma Consolidated Financial Information (Parenthetical) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Business Acquisition [Line Items]
Intangibles amortization	$ 7,854	$ 495	$ 22,358	$ 1,412
Stock based compensation			42,551	34,403
Car Offer
Business Acquisition [Line Items]
Intangibles amortization	7,286	7,275	21,836	21,825
Stock based compensation	$ 1,083	$ 1,083	$ 9,813	$ 9,628

Fair Value of Financial Instr_3

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	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments:	$ 90,000	$ 100,000
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments:	$ 90,000	$ 100,000
Debt Securities Held To Maturity Type Extensible List	us-gaap:CertificatesOfDepositMember	us-gaap:CertificatesOfDepositMember
Total	$ 257,521	$ 212,431
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	167,521	112,431
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:	$ 90,000	$ 100,000
Debt Securities Held To Maturity Type Extensible List	us-gaap:CertificatesOfDepositMember	us-gaap:CertificatesOfDepositMember
Total	$ 90,000	$ 100,000
Fair Value, Measurements, Recurring | Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:	167,521	112,431
Fair Value, Measurements, Recurring | Money Market Funds | Quoted Prices in Active Markets for Identical Assets (Level 1 Inputs)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents:	$ 167,521	$ 112,431

Fair Value of Financial Instr_4

Fair Value of Financial Instruments Including Cash, Cash Equivalents, and Investments - Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Liabilities, fair value	$ 0	$ 0
Maturity period of certificates of deposit	1 year	1 year
Maturity of certificates of deposit, description	Certificates of deposit at September 30, 2021 and at December 31, 2020 had maturity dates of one year or less.

Fair Value of Financial Instr_5

Fair Value of Financial Instruments Including Cash, Cash Equivalents, and Investments - Schedule of Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Certificates of deposit due in one year or less, Amortized Cost	$ 90,000	$ 100,000
Held to maturity amortized cost	90,000	100,000
Certificates of deposit due in one year or less, Estimated Fair Value	90,000	100,000
Held to maturity fair value	$ 90,000	$ 100,000

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 62,056	$ 53,477
Less accumulated depreciation and amortization	(32,487)	(25,994)
Property and equipment, net	29,569	27,483
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	8,604	8,108
Capitalized Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	149	149
Capitalized Website Development
Property Plant And Equipment [Line Items]
Property and equipment, gross	19,451	16,328
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	8,491	7,320
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	24,086	20,507
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	665	1,024
Finance Lease Right-of-use Assets
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 610	$ 41

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Property, Plant and Equipment [Abstract]
Depreciation	$ 2,755,000	$ 1,937,000	$ 7,068,000	$ 7,367,000
Amortization expense of internal-use software	$ 47,000	$ 0	$ 61,000	$ 0

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets - Summary of Changes in Carrying Value of Goodwill (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Balance at December 31, 2020	$ 29,129
CarOffer acquisition	127,500	[1]
Foreign currency translation adjustment	(922)
Balance at June 30, 2021	$ 155,707
[1]	See Note 4 of the Unaudited Condensed Consolidated Financial Statements included elsewhere in this Quarterly Report.

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Impairment of goodwill					$ 0
Amortization expense of intangible assets	$ 7,854,000	$ 495,000	$ 22,358,000	$ 1,412,000
Impairment of intangible assets					$ 0

Goodwill and Other Intangible_5

Goodwill and Other Intangible Assets - Summary of Other Intangible Assets (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 117,421	$ 13,504
Accumulated Amortization	25,000	2,642
Net Carrying Amount	$ 92,421	$ 10,862
Brand
Finite Lived Intangible Assets [Line Items]
Weighted Average Remaining Useful Life (years)	9 years 7 months 6 days	8 years 4 months 24 days
Gross Carrying Amount	$ 32,338	$ 9,405
Accumulated Amortization	3,444	1,235
Net Carrying Amount	$ 28,894	$ 8,170
Customer Relationships
Finite Lived Intangible Assets [Line Items]
Weighted Average Remaining Useful Life (years)	2 years 2 months 12 days	1 year 7 months 6 days
Gross Carrying Amount	$ 19,871	$ 1,886
Accumulated Amortization	5,660	938
Net Carrying Amount	$ 14,211	$ 948
Developed Technology
Finite Lived Intangible Assets [Line Items]
Weighted Average Remaining Useful Life (years)	2 years 3 months 18 days	1 year
Gross Carrying Amount	$ 65,212	$ 2,213
Accumulated Amortization	15,896	469
Net Carrying Amount	$ 49,316	$ 1,744

Goodwill and Other Intangible_6

Goodwill and Other Intangible Assets - Summary of Estimated Amortization Expense of Intangible Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Remainder of 2021	$ 7,874
2022	31,078
2023	30,350
2024	4,144
2025	3,052
2026	3,052
Thereafter	12,871
Net Carrying Amount	$ 92,421	$ 10,862

Accrued Expenses, Accrued Inc_3

Accrued Expenses, Accrued Income Taxes and Other Current Liabilities - Schedule of Accrued Expenses, Accrued Income Taxes and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accrued Liabilities, Current [Abstract]
Accrued bonus	$ 7,372	$ 10,845
Accrued commissions	2,841	3,941
Other accrued expenses and other current liabilities	11,709	9,965
Total	$ 21,922	$ 24,751

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	Jan. 25, 2021USD ($)ft²	Jul. 01, 2019USD ($)ft²	Sep. 30, 2021USD ($)	Dec. 31, 2020USD ($)
Commitments And Contingencies [Line Items]
Operating lease right-of-use assets			$ 63,841,000	$ 60,835,000
Restricted cash			$ 16,130,000	$ 10,627,000
Car Offer | Addison, Texas at 15601 Dallas Parkway
Commitments And Contingencies [Line Items]
Operating lease, office space | ft²	61,826
Sublease term description			non-cancellable lease term through 2030
Sublease commencement date	Mar. 1, 2021
Sublease rent commencement date	Jan. 1, 2022
Sublease monthly base rent payable	$ 152,000
Increase in sublease monthly base rent, maximum amount payable	$ 185,000
Car Offer | Addison, Texas at 15601 Dallas Parkway | Furniture and Fixtures
Commitments And Contingencies [Line Items]
Operating lease right-of-use assets percentage	5.00%
Operating lease right-of-use assets	$ 664,000
Car Offer | Addison, Texas at 15601 Dallas Parkway | Office Space
Commitments And Contingencies [Line Items]
Operating lease right-of-use assets percentage	95.00%
Operating lease right-of-use assets	$ 12,336,000
Car Offer | Plano, Texas at 2701 East Plano Parkway
Commitments And Contingencies [Line Items]
Operating lease, office space | ft²		26,971
Sublease term description			non-cancellable lease term through 2023
Sublease commencement date		Jul. 1, 2019
Sublease rent commencement date		Jul. 1, 2019
Sublease monthly base rent payable		$ 21,000
Increase in sublease monthly base rent, maximum amount payable		$ 22,000

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Capitalized website development and internal-use software costs excluded from stock-based compensation expense	$ 777	$ 656		$ 2,212	$ 1,323
Total payments for employees' tax obligations to taxing authorities due to net share settlements and cashless exercises of options	$ 3,106	$ 2,922		$ 11,314	$ 8,708
Class A Common Stock
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Employee tax withholding requirements and option costs due to net share settlement	114,973	111,370	119,009	404,626	337,313
2020 CO Plan
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of shares authorized for issuances	485,714			485,714
2021 CO Plan
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Number of shares authorized for issuances	228,571			228,571

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Stock-based Compensation Expense by Award Type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 15,169	$ 11,030	$ 53,102	$ 34,634
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	630		1,882	17
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	13,852	$ 11,030	41,539	$ 34,617
CarOffer Incentive Units and Subject Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 687		$ 9,681

Stock-based Compensation - Su_2

Stock-based Compensation - Summary of Allocation of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 15,169	$ 11,030	$ 53,102	$ 34,634
Cost of Revenue
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	110	57	311	241
Sales and Marketing Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	2,717	2,450	9,040	8,206
Product, Technology, and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	5,583	5,140	17,585	15,861
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 6,759	$ 3,383	$ 26,166	$ 10,326

Earnings Per Share - Additional

Earnings Per Share - Additional Information (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021shares	Sep. 30, 2020shares	Sep. 30, 2021Voteshares	Sep. 30, 2020shares
Earnings Per Share Basic [Line Items]
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 upon either the death or voluntary termination of the Company’s Executive Chairman.
Undistributed earnings ratio used to calculate allocation to class of stock			100.00%
Market Based Performance Awards
Earnings Per Share Basic [Line Items]
Potentially dilutive common stock equivalents excluded from calculation of diluted weighted-average shares outstanding	282,921		282,921
Class A Common Stock
Earnings Per Share Basic [Line Items]
Right to voting			one vote per share
Number of votes entitled to stockholders per share | Vote			1
Conversion of stock	1,676,061	898,655	2,605,658	1,238,144
Class B Common Stock
Earnings Per Share Basic [Line Items]
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 o

Earnings Per Share - Schedule of Reconciliation of Numerator and Denominator Used in Calculation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Consolidated net income	$ 29,267	$ 32,563	$ 76,214	$ 52,390
Less: Net income (loss) attributable to redeemable noncontrolling interest	68		(3,398)
Net income attributable to common stockholders - basic	29,199	32,563	79,612	52,390
Add: Net income (loss) attributable to redeemable noncontrolling interest	68		(588)
Net income attributable to common stockholders — diluted	$ 29,267	$ 32,563	$ 79,024	$ 52,390
Denominator:
Weighted-average number of shares of common stock used in computing net income per share attributable to common stockholders — basic	117,412,164	113,027,995	116,955,188	112,707,003
Dilutive effect of share equivalents resulting from stock options	418,054	632,581	460,553	701,176
Dilutive effect of share equivalents resulting from unvested restricted stock units	491,175	306,287	403,967	324,437
Dilutive effect of share equivalents resulting from CarOffer incentive units and noncontrolling interest	2,116,980		1,231,520
Weighted-average number of shares of common stock used in computing net income per share attributable to common stockholders — diluted	120,438,373	113,966,863	119,051,228	113,732,616
Net income per share attributable to common stockholders:
Basic	$ 0.25	$ 0.29	$ 0.68	$ 0.46
Diluted	$ 0.24	$ 0.29	$ 0.66	$ 0.46

Earnings Per Share - Schedule_2

Earnings Per Share - Schedule of Potentially Dilutive Common Stock Equivalents Excluded from Calculation of Diluted Weighted-average Shares Outstanding (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
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	588,490		501,306
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	2,181,061	2,577,713	2,507,873	2,893,491

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Tax Examination [Line Items]
Income tax provision (benefit)	$ 10,952	$ 11,209	$ 28,556	$ 13,312
Effective income tax rate	27.30%	25.60%	26.40%	20.30%
Statutory tax rate	21.00%	21.00%	21.00%	21.00%
New York | Earliest Tax Year
Income Tax Examination [Line Items]
Income tax sales tax audit year			2014
New York | Latest Tax Year
Income Tax Examination [Line Items]
Income tax sales tax audit year			2020
UK Revenue Agency | Foreign
Income Tax Examination [Line Items]
Open tax year			2018
Canada Revenue Agency | Foreign
Income Tax Examination [Line Items]
Open tax year			2018
Revenue Commissioners, Ireland | Foreign
Income Tax Examination [Line Items]
Open tax year			2018
Internal Revenue Service (IRS) | State
Income Tax Examination [Line Items]
Closed tax year			2017
Internal Revenue Service (IRS) | Domestic Tax Authority
Income Tax Examination [Line Items]
Closed tax year			2017

Segment and Geographic Inform_3

Segment and Geographic Information - Additional Information (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)Segment	Dec. 31, 2020USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | Segment	2
Assets	$ 819,917	$ 502,298
Goodwill	155,707	29,129
International
Segment Reporting Information [Line Items]
Assets	33,877	32,012
Goodwill	$ 15,728	$ 16,652

Segment and Geographic Inform_4

Segment and Geographic Information - Summary of Operations by Segment and Geographical Area (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment revenue:
Revenue	$ 222,915	$ 147,472	$ 612,031	$ 399,898
Segment income (loss) from operations:
Total income from operations	40,076	43,567	104,344	64,295
United States
Segment revenue:
Revenue	211,554	138,412	581,149	376,164
Segment income (loss) from operations:
Total income from operations	41,931	46,462	111,515	82,061
International
Segment revenue:
Revenue	11,361	9,060	30,882	23,734
Segment income (loss) from operations:
Total income from operations	$ (1,855)	$ (2,895)	$ (7,171)	$ (17,766)