100000 - Document - Document and Entity Information link:presentationLink link:calculationLink link:definitionLink 100010 - Statement - Unaudited Condensed Consolidated Balance Sheets link:presentationLink link:calculationLink link:definitionLink 100020 - Disclosure - Accrued Expenses, Accrued Income Taxes and Other Current Liabilities - Schedule of Accrued Expenses, Accrued Income Taxes and Other Current Liabilities (Details) 2 link:presentationLink link:calculationLink link:definitionLink 100030 - Statement - Unaudited Condensed Consolidated Balance Sheets (Parenthetical) link:presentationLink link:calculationLink link:definitionLink 100040 - Statement - Unaudited Condensed Consolidated Income Statements link:presentationLink link:calculationLink link:definitionLink 100050 - Statement - Unaudited Condensed Consolidated Income Statements (Parenthetical) link:presentationLink link:calculationLink link:definitionLink 100060 - Statement - Unaudited Condensed Consolidated Statements of Comprehensive Income link:presentationLink link:calculationLink link:definitionLink 100070 - Statement - Unaudited Condensed Consolidated Statements of Redeemable Noncontrolling Interest and Stockholders' Equity link:presentationLink link:calculationLink link:definitionLink 100080 - Statement - Unaudited Condensed Consolidated Statements of Cash Flows link:presentationLink link:calculationLink link:definitionLink 995455 - Disclosure - Organization and Business Description link:presentationLink link:calculationLink link:definitionLink 995465 - Disclosure - Summary of Significant Accounting Policies link:presentationLink link:calculationLink link:definitionLink 995475 - Disclosure - Revenue Recognition link:presentationLink link:calculationLink link:definitionLink 995485 - Disclosure - Fair Value of Financial Instruments link:presentationLink link:calculationLink link:definitionLink 995495 - Disclosure - Property and Equipment, Net link:presentationLink link:calculationLink link:definitionLink 995505 - Disclosure - Goodwill and Other Intangible Assets link:presentationLink link:calculationLink link:definitionLink 995515 - Disclosure - Accrued Expenses, Accrued Income Taxes and Other Current Liabilities link:presentationLink link:calculationLink link:definitionLink 995525 - Disclosure - Debt link:presentationLink link:calculationLink link:definitionLink 995535 - Disclosure - Commitments and Contingencies link:presentationLink link:calculationLink link:definitionLink 995545 - Disclosure - Stock-based Compensation and Common Stock Share Repurchases link:presentationLink link:calculationLink link:definitionLink 995555 - Disclosure - Earnings Per Share link:presentationLink link:calculationLink link:definitionLink 995565 - Disclosure - Income Taxes link:presentationLink link:calculationLink link:definitionLink 995575 - Disclosure - Segment and Geographic Information link:presentationLink link:calculationLink link:definitionLink 995585 - Disclosure - Summary of Significant Accounting Policies (Policies) link:presentationLink link:calculationLink link:definitionLink 995595 - Disclosure - Revenue Recognition (Tables) link:presentationLink link:calculationLink link:definitionLink 995605 - Disclosure - Fair Value of Financial Instruments (Tables) link:presentationLink link:calculationLink link:definitionLink 995615 - Disclosure - Property and Equipment, Net (Tables) link:presentationLink link:calculationLink link:definitionLink 995625 - Disclosure - Goodwill and Other Intangible Assets (Tables) link:presentationLink link:calculationLink link:definitionLink 995635 - Disclosure - Accrued Expenses, Accrued Income Taxes and Other Current Liabilities (Tables) link:presentationLink link:calculationLink link:definitionLink 995645 - Disclosure - Commitments and Contingencies (Tables) link:presentationLink link:calculationLink link:definitionLink 995655 - Disclosure - Stock-based Compensation and Common Stock Share Repurchases (Tables) link:presentationLink link:calculationLink link:definitionLink 995665 - Disclosure - Earnings Per Share (Tables) link:presentationLink link:calculationLink link:definitionLink 995675 - Disclosure - Segment and Geographic Information (Tables) link:presentationLink link:calculationLink link:definitionLink 995685 - Disclosure - Organization and Business Description - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 995695 - Disclosure - Summary of Significant Accounting Policies - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 995705 - Disclosure - Revenue Recognition - Summary of Revenue from Contracts with Customers by Services and Products (Details) link:presentationLink link:calculationLink link:definitionLink 995715 - Disclosure - Revenue Recognition - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 995725 - Disclosure - Fair Value of Financial Instruments - Schedule of Fair Value Levels, Assets Measured at Fair Value on Recurring Basis (Details) link:presentationLink link:calculationLink link:definitionLink 995735 - Disclosure - Fair Value of Financial Instruments - Summary of Unrealized Gain on Investments in Equity Securities (Details) link:presentationLink link:calculationLink link:definitionLink 995745 - Disclosure - Fair Value of Financial Instruments - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 995755 - Disclosure - Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) link:presentationLink link:calculationLink link:definitionLink 995765 - Disclosure - Property and Equipment, Net - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 995775 - Disclosure - Accrued Expenses, Accrued Income Taxes and Other Current Liabilities - Schedule of Accrued Expenses, Accrued Income Taxes and Other Current Liabilities (Details) link:presentationLink link:calculationLink link:definitionLink 995785 - Disclosure - Accrued Expenses, Accrued Income Taxes and Other Current Liabilities - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 995795 - Disclosure - Debt - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 995805 - Disclosure - Commitments and Contingencies - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 995815 - Disclosure - Stock-based Compensation and Common Stock Share Repurchases - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 995825 - Disclosure - Stock-based Compensation and Common Stock Share Repurchases - Summary of Stock-based Compensation Expense by Award Type (Details) link:presentationLink link:calculationLink link:definitionLink 995835 - Disclosure - Stock-based Compensation and Common Stock Share Repurchases - Summary of Allocation of Stock-based Compensation Expense (Details) link:presentationLink link:calculationLink link:definitionLink 995845 - Disclosure - Earnings Per Share - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 995855 - Disclosure - Earnings Per Share - Schedule of Reconciliation of Numerator and Denominator Used in Calculation of Basic and Diluted Net Income Per Share (Details) link:presentationLink link:calculationLink link:definitionLink 995865 - Disclosure - Earnings Per Share - Schedule of Potentially Dilutive Common Stock Equivalents Excluded from Calculation of Diluted Weighted-average Shares Outstanding (Details) link:presentationLink link:calculationLink link:definitionLink 995875 - Disclosure - Income Taxes - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 995885 - Disclosure - Segment and Geographic Information - Additional Information (Details) link:presentationLink link:calculationLink link:definitionLink 995895 - Disclosure - Segment and Geographic Information - Summary of Segment Revenue, Income (Loss) and Depreciation and Amortization (Details) link:presentationLink link:calculationLink link:definitionLink 995905 - Disclosure - Segment and Geographic Information - Summary of Reconciliation Between Segment Income from Operations (Details) link:presentationLink link:calculationLink link:definitionLink 995915 - Disclosure - Segment and Geographic Information - Summary of Assets by Segment (Details) link:presentationLink link:calculationLink link:definitionLink 995925 - Disclosure - Segment and Geographic Information - Summary of Revenue by Geographical Region (Details) link:presentationLink link:calculationLink link:definitionLink Accounts Receivable, before Allowance for Credit Loss, Current Trade accounts receivable from receivables in transit, net of payables due, from the third-party payment processor Collaborative Arrangement and Arrangement Other than Collaborative [Domain] Document Transition Report Document Transition Report Revenue, Remaining Performance Obligation, Amount Performance obligation unsatisfied Mutual funds Money Market Funds [Member] Option Indexed to Issuer's Equity [Axis] Geographical [Axis] Geographical Unrealized Gain (Loss) on Investments Unrealized gain on investments Distributions to redeemable noncontrolling interest holders Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests Total Other Liabilities, Noncurrent Other non–current liabilities Schedule of Segment Reporting Information, by Segment [Table] Schedule Of Segment Reporting Information By Segment [Table] Increase (Decrease) in Prepaid Expense and Other Assets, Total Increase (Decrease) in Prepaid Expense and Other Assets Prepaid expenses, prepaid income taxes, and other assets Increase in borrowing capacity equal to percentage of four quarter EBDITA Increase In Borrowing Capacity Equal To Percentage Of Four Quarter EBDITA Increase in borrowing capacity equal to percentage of four quarter EBDITA. Valuation of redeemable noncontrolling interest Redeemable Noncontrolling Interest, Equity, Carrying Amount Redeemable Noncontrolling Interest, Ending balance Redeemable Noncontrolling Interest, Beginning balance Redeemable noncontrolling interest Redeemable Noncontrolling Interest, Equity, Carrying Amount, Total Restricted Stock Units (RSUs) [Member] Restricted Stock Units Restricted Stock Units Outstanding Fair Value, Inputs, Level 1 [Member] Quoted Prices in Active Markets for Identical Assets (Level 1 Inputs) Receivable Type [Axis] Wholesale Wholesale [Member] Wholesale [Member] Mutual Funds Mutual Fund [Member] Income Tax, Policy [Policy Text Block] Income Taxes Total Revenue Revenue from Contract with Customer, Excluding Assessed Tax, Total Revenue Total Revenue Payment of tax distributions to redeemable noncontrolling interest holders Payment of tax distribution to redeemable noncontrolling interest holders Payment of Tax Distribution to Redeemable Noncontrolling Interest Holders Payment of tax distribution to redeemable noncontrolling interest holders. Summary of Revenue from Contracts with Customers by Services and Products Disaggregation of Revenue [Table Text Block] Concentration Risk Type [Axis] Concentration Risk Type Short-Term Debt, Type [Axis] Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Organization and Business Description Contract with Customer, Liability, Current Deferred revenue Share-Based Payment Arrangement, Cost by Plan [Table Text Block] Summary of Stock-based Compensation Expense by Award Type Operating Lease, Liability, Noncurrent Operating lease liabilities Stock Repurchased During Period, Shares Repurchase of common stock, Shares Reconciliation of Assets from Segment to Consolidated [Table Text Block] Summary of Assets by Segment Accounts Receivable and Other Receivables Accounts Receivable And Other Receivables [Member] Accounts receivable and other receivables Depreciation and amortization excluding amortization of intangible assets, capitalized hosting arrangements and impairments Depreciation and Amortization Excluding Amortization of Intangible Assets, Capitalized Hosting Arrangements and impairments Depreciation and amortization excluding amortization of intangible assets, capitalized hosting arrangements and impairments Stock Issued During Period, Value, Conversion of Convertible Securities, Net of Adjustments, Total Stock Issued During Period, Value, Conversion of Convertible Securities, Net of Adjustments Conversion of common stock Balance Sheet Location [Axis] Assets, Current Total current assets Unpaid withholding taxes on net share settlement of restricted stock units Unpaid Withholding Taxes On Net Share Settlement Of Restricted Stock Units Unpaid withholding taxes on net share settlement of restricted stock units Liabilities and Equity Total liabilities, redeemable noncontrolling interest and stockholders’ equity Entity Address, State or Province Entity Address, State or Province Receivables offset by payments received in advance Receivables Offset By Payments Received In Advance Receivables offset by payments received In advance. Deferred Income Tax Assets, Net Deferred tax assets Deferred Income Tax Assets, Net, Total Comprehensive income attributable to common stockholders Comprehensive Income (Loss), Net of Tax, Attributable to Parent Goodwill and Intangible Assets, Policy [Policy Text Block] Goodwill and Other Intangible Assets Trading Symbol Trading Symbol Common Stock, Shares, Issued, Total Common Stock, Shares, Issued Common stock, shares issued Prepaid Expense and Other Assets, Current Prepaid expenses, prepaid income taxes and other current assets Net Income (Loss) Attributable to Parent [Abstract] Numerator: San Francisco and Cambridge. San Francisco and Cambridge [Member[ San Francisco and Cambridge Selling and Marketing Expense [Member] Sales and Marketing Expense Schedule of Long-Term Debt Instruments [Table] Foreign Tax Authority [Member] Foreign AOCI Attributable to Parent [Member] Accumulated Other Comprehensive Loss Investments Equity Securities, FV-NI Equity Securities, FV-NI, Total Entity Address, City or Town Entity Address, City or Town Debt Debt Disclosure [Text Block] Property, Plant and Equipment [Table Text Block] Schedule of Property and Equipment, Net CarOffer. Car Offer [Member] Car Offer Less: Net income (loss) attributable to redeemable noncontrolling interest Net Income (Loss) Attributable to Redeemable Noncontrolling Interest, Total Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Net loss attributable to redeemable noncontrolling interest Subsequent Event [Member] Subsequent Event Subsequent Event Type [Axis] Finance Lease, Principal Payments Payment of finance lease obligations Net income (loss) per share attributable to common stockholders. Net Income (Loss) Per Share Attributable To Common Stockholders Abstract Net income per share attributable to common stockholders: Additional Paid-in Capital [Member] Additional Paid-in Capital Non-US [Member] International Current liabilities: Liabilities, Current [Abstract] Assets, Current [Abstract] Current assets Accounts Receivable, Allowance for Credit Loss, Current Allowance for doubtful accounts Realized gain on short-term investments Gain on Sale of Investments Realized gain on investments Preferred Stock, Par or Stated Value Per Share Preferred stock, par value Statement of Stockholders' Equity [Abstract] Operating Lease, Liability, Current Operating lease liabilities Long-term debt outstanding Long-Term Debt Long-Term Debt, Total Property, Plant and Equipment, Net Property and equipment, net Property and equipment, net Property, Plant and Equipment, Net, Beginning Balance Property, Plant and Equipment, Net, Ending Balance Total Class of Stock [Domain] Class of Stock Acquisition of redeemable noncontrolling interest. Acquisition Of Redeemable Noncontrolling Interest Acquisition of a 51% interest in CarOffer, LLC Investment Income, Interest Interest income Provision (Recoveries) for doubtful accounts Accounts Receivable, Credit Loss Expense (Reversal) Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent Statutory tax rate Statement of Comprehensive Income [Abstract] Collaborative Arrangement and Arrangement Other than Collaborative [Axis] Summary of significant accounting policies. Summary Of Significant Accounting Policies [Table] Summary Of Significant Accounting Policies [Table] Entity Central Index Key Entity Central Index Key Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures, Total Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures Issuance of common stock upon vesting of restricted stock units Increase decrease in lease obligations. Increase Decrease In Lease Obligations Lease obligations Depreciation and amortization expense Cost Of Goods And Services Sold Depreciation Amortization And Impairment Expense Cost of goods and services sold depreciation amortization and impairment expense. Digital Wholesale and U.S. Marketplace Digital Wholesale And United States Marketplace[member] Digital wholesale and united states marketplace. Restricted Cash, Noncurrent Restricted cash Stock repurchase program effective date. Stock Repurchase Program Effective Date Share repurchase program effective date Assets, Fair Value Disclosure Total Assets, Fair Value Disclosure, Total Schedule of Accrued Expenses, Accrued Income Taxes and Other Current Liabilities Schedule Of Accrued Liabilities And Other Current Liabilities Table [Text Block] Schedule of accrued liabilities and other current liabilities. Accretion of redeemable noncontrolling interest to redemption value Redeemable Noncontrolling Interest Accretion to Redemption Value Redeemable noncontrolling interest accretion to redemption value. Preferred Stock, Shares Outstanding Preferred stock, shares outstanding Preferred Stock, Shares Outstanding, Beginning Balance Preferred Stock, Shares Outstanding, Ending Balance Schedule of Goodwill [Table Text Block] Summary of Changes in Carrying Value of Goodwill Payment of withholding taxes on net share settlements of restricted stock units. Payment Of Withholding Taxes On Net Share Settlements Of Restricted Stock Units Payment of withholding taxes on net share settlements of restricted stock units Payment of withholding taxes on net share settlements of restricted stock units Liabilities, Current Total current liabilities Entity Tax Identification Number Entity Tax Identification Number Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table] Increase (Decrease) in Operating Capital [Abstract] Changes in operating assets and liabilities: Payments of Debt Issuance Costs Payment of deferred financing costs Construction in Progress [Member] Construction in Progress Conversion of Stock, Description Conversion of stock, description Geographical [Domain] Geographical Assets Assets Total assets Summary of Revenue by Geographical Region Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block] UNITED STATES United States Operating Lease, Right-of-Use Asset Operating lease right-of-use assets Common Class A [Member] Class A Common Stock Entity Registrant Name Entity Registrant Name Deferred financing costs Debt Issuance Costs, Net Debt Issuance Costs, Net, Total Retained Earnings (Accumulated Deficit), Total Retained Earnings (Accumulated Deficit), Beginning Balance Retained Earnings (Accumulated Deficit), Ending Balance Retained Earnings (Accumulated Deficit) Retained earnings Summary of Unrealized Gain on Investments in Equity Securities Unrealized Gain (Loss) on Investments [Table Text Block] Supplemental Cash Flow Information [Abstract] Supplemental disclosure of cash flow information: Customer one. Customer One [Member] Customer One Retained Earnings [Member] Retained Earnings Class of Stock [Axis] Class of Stock Deferred Income Tax Liabilities, Net, Total Deferred Income Tax Liabilities, Net Deferred tax liabilities Minimum Minimum [Member] Other Directors and Officers Other Directors and Officers [Member] Other directors and officers. Pillar Two Legislation Pillar Two Legislation [Member] Pillar two legislation Proceeds from Stock Options Exercised Proceeds from issuance of common stock upon exercise of stock options Significant Accounting Policies [Text Block] Summary of Significant Accounting Policies Investments sold Security Sold Short, Fair Value Impairments in capitalized website development costs Capitalized Computer Software, Impairments Closed tax year. Closed Tax Year Closed tax year Accrued Income Taxes, Current Accrued income taxes Equity Component [Domain] Equity Component Segments [Axis] Stock Options Outstanding Disposal Of The Data Center Asset [Member] Disposal Of The Data Center Asset [Member] Disposal of the data center asset Software Development [Member] Capitalized Website Development Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile consolidated net income to net cash provided by operating activities: Measurement Frequency [Axis] Measurement Frequency Debt Disclosure [Abstract] Net Income (Loss) Available to Common Stockholders, Diluted Net income attributable to common stockholders - diluted Share-Based Payment Arrangement, Decrease for Tax Withholding Obligation Payment of withholding taxes on net share settlements of restricted stock units Entity Current Reporting Status Entity Current Reporting Status Common Stock, Shares Authorized Common stock, shares authorized Research and Development Expense, Total Research and Development Expense Product, technology, and development Currency loss (gain) on foreign denominated transactions Unrealized Gain (Loss), Foreign Currency Transaction, before Tax Market based performance award RSU. Market Based Performance Award RSU [Member] Market Based Performance Award RSU Stock Repurchase Program, Authorized Amount Aggregate share repurchase price Assets [Abstract] Assets Boston, Massachusetts one zero zero one Boylston. Boston Massachusetts One Zero Zero One Boylston [Member] Boston, Massachusetts at 1001 Boylston St 1001 Boylston Street Revenue Recognition - Wholesale and Other Revenue and Inventory Revenue from Contract with Customer [Policy Text Block] 2024 Put Right Two Thousand Twenty Four Put Right Member Two Thousand Twenty Four Put Right Member. Fifty five cambridge parkway. Fifty Five Cambridge Parkway [Member] 55 Cambridge Parkway Significant accounting policies. Significant Accounting Policies Policy [Text Block] Significant Accounting Policies Stock Repurchased and Retired During Period, Value Share repurchased and retired, value Common Stock, Value, Issued, Total Common Stock, Value, Issued, Beginning Balance Common Stock, Value, Issued, Ending Balance Common Stock, Value, Issued Common stock Conversion of Stock, Shares Issued Conversion of stock Accounts Payable, Accrued Liabilities, and Other Liabilities Disclosure, Current [Text Block] Schedule of Accrued Expenses, Accrued Income Taxes and Other Current Liabilities Accrued Expenses, Accrued Income Taxes and Other Current Liabilities Other Noncash Income (Expense), Total Other Noncash Income (Expense) Other non-cash expense, net Contract with Customer, Liability, Revenue Recognized Revenue recognized Furniture and Fixtures [Member] Furniture and Fixtures Schedule of future minimum sublease income payments. Schedule of Future Minimum Sublease Income Payments [Table Text Block] Schedule of Future Minimum Sublease Income Payments Current Fiscal Year End Date Current Fiscal Year End Date Share-based Payment Arrangement, Noncash Expense, Total Share-Based Payment Arrangement, Noncash Expense Stock-based compensation expense Stock based compensation Operating Income (Loss) Income from operations Income (Loss) from Operations Total segment income from operations Accounting Standards Update 2019-12 [Member] ASU 2019-12 Tax Period [Axis] Deferred Income Tax Expense (Benefit), Total Deferred Income Tax Expense (Benefit) Deferred taxes Income Tax Expense (Benefit), Total Income Tax Expense (Benefit) Provision for income taxes Income tax provision (benefit) Investment [Table Text Block] Schedule of Investments Research and Development Expense [Member] Product, Technology, and Development Expense Summary of Contractual Obligations Contractual Obligation, Fiscal Year Maturity [Table Text Block] Stock Issued During Period, Shares, Acquisitions Issuance of common stock upon for acquisition, Shares Concentration Risk, Percentage Concentration of credit risk, percentage Total Total Disaggregation of Revenue [Table] Jason Trevisan Jason Trevisan [Member] Jason Trevisan. Equipment [Member] Capitalized Equipment Decrease in lease liability Increase (Decrease) in Operating Lease Liability Finite-Lived Intangible Assets, Net Intangible assets, net Net Carrying Amount Finite-Lived Intangible Assets, Net, Beginning Balance Finite-Lived Intangible Assets, Net, Ending Balance Schedule of Segment Reporting Information, by Segment [Table Text Block] Summary of Segment Revenue, Income (Loss) and Depreciation and Amortization Receivable from sale of property and equipment Receivable From Sale Of Property And Equipment Receivable from sale of property and equipment. Income Taxes Paid Cash paid for income taxes Revenue from Contract with Customer [Text Block] Revenue Recognition Other comprehensive income: Other Comprehensive Income (Loss), Net of Tax [Abstract] Unrealized gains (losses) recognized during the period on equity securities held as of the end of the period Equity Securities, FV-NI, Unrealized Gain (Loss) Equity Securities, FV-NI, Unrealized Gain (Loss), Total Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table] Schedule Of Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Table] Earnings Per Share, Policy [Policy Text Block] Earnings Per Share Accrued Expenses, Accrued Income Taxes and Other Current Liabilities Accrued Expenses Accrued Income Taxes And Other Current Liabilities [Member] Accrued expenses accrued income taxes and other current liabilities Other (expense) income, net Other Nonoperating Income (Expense), Total Other Nonoperating Income (Expense) Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest, Total Comprehensive income (loss) attributable to redeemable noncontrollin interests Comprehensive loss attributable to redeemable noncontrolling interests Operating Expenses [Abstract] Operating expenses: Property, Plant and Equipment [Abstract] Depreciation, Depletion and Amortization, Nonproduction Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction, Total Sales of short-term investments. Sales of Short-Term Investments Sales of short-term investments Conversion of Stock, Type of Stock Converted Class of share converted to another class Commitments and Contingencies Disclosure [Abstract] Other Assets, Noncurrent, Total Other Assets, Noncurrent Other non-current assets Cash paid for interest Interest Paid, Excluding Capitalized Interest, Operating Activities Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] Earnings Per Share Basic [Line Items] Other accrued expenses and other current liabilities. Other Accrued Expenses And Other Current Liabilities Other accrued expenses and other current liabilities Common Class B [Member] Class B Common Stock Rule 10b5-1 Trading Arrangement Rule 10b5-1 Trading Arrangement [Member] Rule 10b5-1 trading arrangement. Equity, Attributable to Parent [Abstract] Stockholders’ equity: Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Depreciation and Amortization Depreciation and Amortization Included in Cost of Revenue and Operating Expenses Depreciation and Amortization Included in Cost of Revenue and Operating Expenses Gain (Loss) on Disposition of Property Plant Equipment, Total Gain (Loss) on Disposition of Property Plant Equipment Gain on sale of property and equipment Line of credit facility maximum borrowing amount Line of Credit Facility, Maximum Borrowing Capacity Total Cost of revenue Cost of Goods and Services Sold Cost of revenue Cost of Goods and Services Sold, Total Earnings Per Share [Abstract] Net income per share attributable to common stockholders: (Note 10) Expected spend amount remaining for construction Expected Spend Amount Remaining For Construction Expected spend amount remaining for construction. Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block] Summary of Future Minimum Lease Payments Document and entity information Document And Entity Information [Table] Document And Entity Information [Table] Accounting Policies [Abstract] Segments [Domain] Stock Repurchase Program Expiration Date Share repurchase program expiration date Liability Class [Axis] Javier Zamora Javier Zamora [Member] Javier Zamora. Concentration Risk, Credit Risk, Policy [Policy Text Block] Concentration of Credit Risk Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Share Based Compensation Arrangement By Share Based Payment Award [Line Items] Proceeds from sale of property and equipment Proceeds from Sale of Oil and Gas Property and Equipment Revolving Credit Facility Revolving Credit Facility [Member] 2022 Revolver Sub-facility Finance lease right-of-use assets. Finance Lease Right Of Use Assets [Member] Finance Lease Right-of-use Assets Earnings Per Share, Basic, Total Earnings Per Share, Basic Basic Customer Concentration Risk [Member] Customer Concentration Risk Commitments and contingencies (Note 8) Commitments and Contingencies Addison texas one five six zero one dallas parkway. Addison Texas One Five Six Zero One Dallas Parkway[Member] Addison Texas at 15601 Dallas Parkway Income Statement [Abstract] Guarantee income Guarantee Income Guarantee income. Increase (decrease) in property and equipment Property, Plant and Equipment, Gross, Period Increase (Decrease) Property, Plant and Equipment, Gross, Period Increase (Decrease), Total Property, Plant and Equipment Disclosure [Text Block] Property and Equipment, Net Car offer purchase agreement member. CarOffer Purchase Agreement [Member] CarOffer Purchase Agreement Statistical Measurement [Domain] Unbilled Receivables, Current Unbilled accounts receivable Net Cash Provided by (Used in) Operating Activities Net cash provided by operating activities Document Period End Date Document Period End Date Statistical Measurement [Axis] Commitments and Contingencies Disclosure [Text Block] Commitments and Contingencies Operating Lease, Payments Cash paid for operating lease liabilities Earnings Per Share, Diluted Diluted Earnings Per Share, Diluted, Total Tenant improvement allowance reimbursements. Tenant Improvement Allowance Reimbursements Tenant improvement allowance reimbursements Product and Service [Domain] Product and Service Line of credit facility increased in maximum borrowing capacity Line Of Credit Facility Increased in Maximum Borrowing Capacity Line of credit facility increased in maximum borrowing capacity. Cost of Sales [Member] Cost of Revenue Concentration Risk Benchmark [Domain] Concentration Risk Benchmark Internal Revenue Service Internal Revenue Service (IRS) [Member] Revenue from Contract with Customer [Abstract] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV Open Tax Year Open tax year Undistributed earnings ratio used to calculate allocation to class of stock. Undistributed Earnings Ratio Used To Calculate Allocation To Class Of Stock Undistributed earnings ratio used to calculate allocation to class of stock Customer Two Customer Two [Member] Customer two. Fair Value, Recurring [Member] Fair Value, Measurements, Recurring Number of Reportable Segments Number of reportable segments Proceeds from sale of investments. Proceeds from Sale of Investments Sales of investments Additional Paid in Capital, Common Stock Additional paid-in capital Additional Paid in Capital, Common Stock, Beginning Balance Additional Paid in Capital, Common Stock, Ending Balance CO Incentive Units Car Offer Incentive Units [Member] CarOffer incentive units. Net gain (loss) recognized during the period on equity securities Equity Securities, FV-NI, Realized Gain (Loss) Equity Securities, FV-NI, Realized Gain (Loss), Total Short-term investments Equity Securities, FV-NI, Current Advance Payments to Customer, Net of Collections Advance payments to customer, net of collections. Advance payments to customers, net of collections Cost of Goods and Services Sold [Abstract] Cost of revenue Repurchases of common stock Payments for Repurchase of Common Stock Investment, Type [Extensible Enumeration] Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period Issuance of common stock upon exercise of stock options, Shares Consolidation, Policy [Policy Text Block] Principles of Consolidation Liabilities and Equity [Abstract] Liabilities, redeemable noncontrolling interest and stockholders’ equity Unpaid excise tax on repurchases of common stock Unpaid Excise Tax On Repurchases Of Shares Unpaid excise tax on repurchases of shares. Schedule of Earnings Per Share, Basic, by Common Class, Including Two Class Method [Table] Schedule Of Earnings Per Share Basic By Common Class [Table] Schedule of Other Non-Current Liabilities Other Noncurrent Liabilities [Table Text Block] Capitalized Computer Software, Period Increase (Decrease), Total Capitalized Computer Software, Period Increase (Decrease) Capitalized equipment decreased Stock Issued During Period, Value, Acquisitions Issuance of common stock upon for acquisition Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Interactive Data Current Entity Interactive Data Current Selling and Marketing Expense Sales and marketing Selling and Marketing Expense, Total Increase (Decrease) in Accounts Payable Accounts payable Increase (Decrease) in Accounts Payable, Total Credit Facility [Domain] Number of major customers. Number Of Major Customers Number of major customers Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code State of incorporation Equity Components [Axis] Accumulated Other Comprehensive Income (Loss) Increase (Decrease) in Accounts Receivable Accounts receivable Other Segments [Member] Other Increase (Decrease) in Contract with Customer, Asset Deferred contract costs Local Phone Number Local Phone Number Property, Plant and Equipment [Line Items] Property Plant And Equipment [Line Items] Share repurchased and retired at average cost price per share. Share Repurchased And Retired At Average Cost Price Per Share Share repurchased and retired at average cost price per share Line of credit facility decreased in maximum borrowing capacity. Line Of Credit Facility Decreased In Maximum Borrowing Capacity Line of credit facility decreased in maximum borrowing capacity Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures, Total Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures Issuance of common stock upon vesting of restricted stock units, Shares Gain or loss investments in equity securities Less: Net gains recognized during the period on equity securities sold during the period Equity Securities, FV-NI, Gain (Loss) Equity Securities, FV-NI, Gain (Loss), Total Goodwill Balance at June 30, 2021 Goodwill, Total Balance at December 31, 2020 Goodwill Restricted Cash, Current Restricted cash Statement of Cash Flows [Abstract] Incremental Common Shares Attributable to Dilutive Effect of Equity Unit Purchase Agreements Dilutive effect of share equivalents resulting from unvested restricted stock units CO Incentive Units and Subject Units Car Offer Incentive Units and Subject Units [Member] CarOffer incentive units and subject units. Stock Repurchased and Retired During Period, Shares Number of shares repurchased and retired Sell My Car - Instant Max Cash Offer Sell My Car - Instant Max Cash Offer [Member] Sell My Car - Instant Max Cash Offer. Income Tax Authority [Domain] Income Tax Authority Organization, Consolidation and Presentation of Financial Statements [Abstract] Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax, Total Accumulated Other Comprehensive Income (Loss), Net of Tax Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Gross Profit Gross profit Concentration Risk Benchmark [Axis] Concentration Risk Benchmark Capitalized stock-based compensation expense in website development and internal-use software costs and hosting arrangements Share-Based Payment Arrangement, Amount Capitalized Capitalized website development and internal-use software costs excluded from stock-based compensation expense Common Stock, Par or Stated Value Per Share Common stock, par value Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations Impact of foreign currency on cash, cash equivalents, and restricted cash Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations, Total Long-Lived Tangible Asset [Axis] Long-Lived Tangible Asset Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table] Maximum Maximum [Member] Non Rule 10b 51 Arr Modified Flag Non Rule 10b 51 Arr Modified Flag Fair Value, Inputs, Level 3 [Member] Significant Unobservable Inputs (Level 3 Inputs) APIC, Share-based Payment Arrangement, Increase for Cost Recognition, Total APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Stock–based compensation expense Fair Value, Recurring and Nonrecurring [Table] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table] Short-Term Debt, Type [Domain] Redeemable noncontrolling interest. Redeemable Noncontrolling Interest Policy [Text Block] Redeemable Noncontrolling Interest Net decrease in cash, cash equivalents, and restricted cash Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Payables and Accruals [Abstract] Other Interest and Dividend Income Operating lease, decrease in right-of-use asset due to re-measurement from lease amendment Operating Lease, Decrease in Right-Of-Use Asset Due to Re-Measurement From Lease Amendment Operating lease, decrease in right-of-use asset due to re-measurement from lease amendment. General and Administrative Expense General and Administrative Expense [Member] Redeemable noncontrolling interest , accretion to redemption value Noncontrolling Interest, Change in Redemption Value Supplemental noncash disclosure of cash flow information: Noncash Investing and Financing Items [Abstract] Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements Dilutive effect of share equivalents resulting from stock options Incremental Common Shares Attributable to Share-based Payment Arrangements, Total Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Schedule of Potentially Dilutive Common Stock Equivalents Excluded from Calculation of Diluted Weighted-average Shares Outstanding Segment Reporting Disclosure [Text Block] Segment and Geographic Information City Area Code City Area Code Inventory, Net Inventory, Net, Total Inventory Net Cash Provided by (Used in) Operating Activities [Abstract] Operating Activities Letter of Credit Facility Letter of Credit [Member] Common Stock, Voting Rights Right to voting Customer [Domain] Customer Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Less accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment, Total Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment, Beginning Balance Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment, Ending Balance General and Administrative Expense, Total General and Administrative Expense General and administrative Weighted Average Number of Shares Outstanding, Basic, Total Weighted Average Number of Shares Outstanding, Basic Basic Weighted-average number of shares of common stock used in computing net income per share attributable to common stockholders — basic Guarantor Obligations, Maximum Exposure, Undiscounted Maximum potential amount of future payments required to make under guarantees Financing Activities Net Cash Provided by (Used in) Financing Activities [Abstract] Number of days guarantee period Number Of Days Guarantee Period Number of days guarantee period. Statement [Table] Statement [Table] Advertising customers. Advertising Customers [Member] Advertising Customers Accounts Receivable [Member] Accounts Receivable Net Accounts Receivable One zero zero one boylston street and cambridge. One Zero Zero One Boylston Street and Cambridge [Member] 1001 Boylston Street and Cambridge Increase (Decrease) in Contract with Customer, Liability Deferred revenue Document Fiscal Period Focus Document Fiscal Period Focus Fair Value of Financial Instruments Financial Instruments Disclosure [Text Block] Statement [Line Items] Statement [Line Items] Accrued repurchases of common stock, including excise taxes Accrued repurchases of common stock Accrued Repurchases Of Common Stock Accrued repurchases of common stock. Obtaining a right-of-use asset in exchange for an operating lease liability Obtaining a right-of-use asset in exchange for an operating lease liability Right-of-Use Asset Increase (Decrease) Obtained in Exchange for Operating Lease Liability Right-of-use asset increase (decrease) obtained in exchange for operating lease liability. Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Potentially dilutive common stock equivalents excluded from calculation of diluted weighted-average shares outstanding Capitalized Internal-Use Software Software and Software Development Costs [Member] Letters of credit outstanding Letters of Credit Outstanding, Amount Change in gross advance payments received from third-party payment processor. Change In Gross Advance Payments Received From Third-party Payment Processor Change in gross advance payments received from third-party transaction processor Asset Class [Domain] Asset Class Accounts receivable, net of allowance for doubtful accounts of $610 and $610, respectively Accounts receivable, net Accounts Receivable, after Allowance for Credit Loss, Current Accounts Receivable, after Allowance for Credit Loss, Current, Total Increase (decrease) in accrued liabilities accrued income taxes and other liabilities. Increase Decrease In Accrued Liabilities Accrued Income Taxes And Other Liabilities Accrued expenses, accrued income taxes, and other liabilities Customer [Axis] Customer Common Stock [Member] Common Stock Debt Instrument [Line Items] Redeemable noncontrolling interest, net (loss) income Temporary Equity, Net Income Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value, Total Cash and Cash Equivalents, at Carrying Value, Beginning Balance Cash and Cash Equivalents, at Carrying Value, Ending Balance Stock Repurchased During Period, Value Repurchase of common stock Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Summary of Allocation of Stock-based Compensation Expense Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Proceeds from Sale, Maturity and Collection of Short-Term Investments, Total Proceeds from Sale, Maturity and Collection of Short-Term Investments Maturities of short-term investments Income Tax Examination [Table] Income Tax Examination [Table] Fair Value of Financial Instruments, Policy [Policy Text Block] Fair Value of Financial Instruments Including Cash, Cash Equivalents, and Investments Trade Accounts Receivable Trade Accounts Receivable [Member] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name Summary of significant accounting policies. Summary Of Significant Accounting Policies [Line Items] Summary Of Significant Accounting Policies [Line Items] Cover [Abstract] Document Fiscal Year Focus Document Fiscal Year Focus Option Indexed to Issuer's Equity, Type [Domain] Accrued tax distributions to redeemable noncontrolling interest holders Accrued Tax Distributions To Redeemable Noncontrolling Interest Holders Accrued tax distributions to redeemable noncontrolling interest holders. Share-Based Payment Arrangement [Policy Text Block] Stock-Based Compensation Restructuring Plan [Domain] Decrease in accrued bonus Decrease In Accrued Bonus Decrease in accrued bonus. Segment Reporting [Abstract] Security Exchange Name Security Exchange Name Company's product offerings Company's Product Offerings Company's product offerings. Domestic Tax Authority [Member] Domestic Tax Authority New Accounting Pronouncements, Policy [Policy Text Block] Recent Accounting Pronouncements Adopted Preferred Stock, Shares Issued, Total Preferred Stock, Shares Issued Preferred stock, shares issued Preferred Stock, Shares Authorized Preferred stock, shares authorized Capitalized Expense Property, Plant and Equipment, Gross Property and equipment, gross Property, Plant and Equipment, Gross, Total Property, Plant and Equipment, Gross, Beginning Balance Property, Plant and Equipment, Gross, Ending Balance Commitments and contingencies. Commitments And Contingencies [Line Items] Commitments And Contingencies [Line Items] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree Call Option Call Option [Member] Weighted Average Number of Shares Outstanding, Diluted [Abstract] Denominator: Weighted-average number of shares of common stock used in computing net income per share attributable to common stockholders: Stock Issued During Period, Value, Stock Options Exercised Issuance of common stock upon exercise of stock options Entity Emerging Growth Company Entity Emerging Growth Company Amendment Flag Amendment Flag Capitalized Contract Cost, Amortization Amortization of deferred contract costs Dealer-to-Dealer Dealer-to-Dealer [Member] Dealer-to-Dealer. Accounting Standards Update [Domain] Accounting Standards Update Basis of Accounting, Policy [Policy Text Block] Basis of Presentation Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Summary of Estimated Amortization Expense of Intangible Assets Recent Accounting Pronouncements Not Yet Adopted Recent accounting pronouncements not yet adopted. Recent Accounting Pronouncements Not Yet Adopted Policy [Text Block] Cost of goods and services sold and depreciation and amortization Cost Of Goods And Services Sold And Depreciation and Amortization Depreciation and Amortization Tax Period [Domain] Securities Act File Number Entity File Number Accrued liabilities accrued income taxes and other liabilities current. Accrued Liabilities Accrued Income Taxes And Other Liabilities Current Accrued expenses, accrued income taxes and other current liabilities Total Line of credit facility maturity date Line of Credit Facility, Expiration Date Accounts Payable [Member] Accounts Payable [Member] Goodwill and Intangible Assets Disclosure [Abstract] Share-Based Payment Arrangement [Abstract] Commitments and contingencies. Commitments And Contingencies [Table] Commitments And Contingencies [Table] Accounts payable, net Accounts Payable, Current, Total Accounts Payable, Current Accounts payable Net loss attributable to redeemable noncontrolling interest Net income attributable to redeemable noncontrolling interest Net income loss attributable to redeemable noncontrolling interest dilutive effect. Net Income Loss Attributable To Redeemable Noncontrolling Interest Dilutive Effect Net loss attributable to redeemable noncontrolling interest Operating Expenses Total operating expenses Entity Address, Address Line Two Entity Address, Address Line Two Preferred stock, $0.001 par value per share; 10,000,000 shares authorized; no shares issued and outstanding Preferred Stock, Value, Issued, Total Preferred Stock, Value, Issued, Beginning Balance Preferred Stock, Value, Issued, Ending Balance Preferred Stock, Value, Issued Entity Small Business Entity Small Business Entity Shell Company Entity Shell Company Subsequent Events, Policy [Policy Text Block] Subsequent Event Considerations Investment Type [Axis] Line of credit facility unutilized commitment fee percentage Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Accrued Bonuses, Current Accrued bonus Payments to Acquire Investments, Total Payments to Acquire Investments Purchases of short-term investments Share-Based Payment Arrangement, Shares Withheld for Tax Withholding Obligation Employee tax withholding requirements and option costs due to net share settlement Payment of withholding taxes on net share settlements of restricted stock units, Shares Matthew Quinn Matthew Quinn [Member] Matthew Quinn. Income Tax Examination [Line Items] Income Tax Examination [Line Items] Earnings Per Share [Text Block] Earnings Per Share Revenues [Abstract] Revenue Total revenue Entity Address, Address Line One Entity Address, Address Line One Revenue Benchmark [Member] Sales Revenue, Net Cash and Cash Equivalents, Fair Value Disclosure Cash equivalents: Total Contractual Obligation Contract commitments Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] Antidilutive Securities [Axis] Antidilutive Securities Restricted Cash Restricted cash Restricted Cash, Total Document and entity information. Document And Entity Information [Line Items] Document And Entity Information [Line Items] Line of credit facility commitment fee percentage Line of Credit Facility, Commitment Fee Percentage Subsequent Event Type [Domain] Proceeds from Maturities, Prepayments and Calls of Short-Term Investments Maturities of short-term investments Contract with Customer, Asset, after Allowance for Credit Loss, Noncurrent, Total Contract with Customer, Asset, after Allowance for Credit Loss, Noncurrent Deferred contract costs, net of current portion Income Statement Location [Axis] Income Statement Location Loan receivable Loan receivable Payments to Acquire Loans Receivable Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Consolidated net income Consolidated net income Fair Value, Inputs, Level 2 [Member] Significant Other Observable Inputs (Level 2 Inputs) Product Product [Member] Unpaid repurchases of common stock. Unpaid Repurchases Of Common Stock Unpaid repurchases of common stock Depreciation, Depletion and Amortization Depreciation and amortization Depreciation, Depletion and Amortization, Total Product and Service [Axis] Product and Service Segment Reporting Information, Revenue for Reportable Segment [Abstract] Revenue by Geographic Region: Title of 12(b) Security Title of 12(b) Security Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Table Text Block] Summary of Reconciliation Between Segment Income from Operations Payments to Develop Software Capitalization of website development costs Market based performance awards. Market Based Performance Awards [Member] Market Based Performance Awards Digital wholesale member. Digital Wholesale [Member] Digital Wholesale Schedule of Finite-Lived Intangible Assets [Table Text Block] Summary of Other Intangible Assets Income Tax Authority, Name [Axis] Income Tax Authority, Name Fair Value, Assets Measured on Recurring Basis [Table Text Block] Schedule of Fair Value Levels, Assets Measured at Fair Value on Recurring Basis Investments [Domain] Accounting Standards Update [Axis] Accounting Standards Update Prepaid Expenses, Prepaid Income Taxes and Other Current Assets Prepaid Expenses and Other Current Assets [Member] Cash, Cash Equivalents, and Investments Cash, Cash Equivalents and Investments [Policy Text Block] Cash, cash equivalents and investments. Net Cash Provided by (Used in) Investing Activities [Abstract] Investing Activities Amortization of deferred financing costs Amortization of Debt Issuance Costs State and Local Jurisdiction [Member] State Letter of credit facility Long-Term Line of Credit Long-Term Line of Credit, Total Long-Lived Tangible Asset [Domain] Long-Lived Tangible Asset Number of votes entitled to stockholders per share. Number Of Votes Entitled To Stockholders Per Share Number of votes entitled to stockholders per share Inventory Inventory Increase (Decrease) in Inventories Increase (Decrease) in Inventories, Total Receivable [Domain] Stock Repurchase Program, Remaining Authorized Repurchase Amount Remaining value of authorized shares repurchased Restructuring Plan [Axis] Common Stock, Shares, Outstanding Ending balance, Shares Beginning balance, Shares Common stock, shares outstanding Share-Based Payment Arrangement [Text Block] Stock-based Compensation and Common Stock Share Repurchases Concentration Risk Type [Domain] Concentration Risk Type Income Statement Location [Domain] Income Statement Location Accounts Receivable and Loan Receivables Accounts Receivable and Loan Receivables [Member] Accounts receivable and loan receivables. Document Type Document Type Stock Issued During Period, Shares, Conversion of Convertible Securities Conversion of common stock, shares issued Rule 10b 51 Arr Modified Flag Rule 10b 51 Arr Modified Flag Fair Value by Liability Class [Domain] Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Increase in accrued repurchase of common stock Increase in Accrued Repurchase of Common Stock Increase in accrued repurchase of common stock. Document Quarterly Report Document Quarterly Report Concentration Risk, Credit Risk, Financial Instruments, off-Balance-Sheet Risk Description of significant off-balance sheet risk Goodwill and Intangible Assets Disclosure [Text Block] Goodwill and Other Intangible Assets Revenue Commissioners, Ireland [Member] Revenue Commissioners, Ireland Net Income (Loss) Available to Common Stockholders, Basic Net income attributable to common stockholders - basic Trd Arr Expiration Date Trd Arr Expiration Date Property and Equipment, Net Property, Plant and Equipment [Member] Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Net cash used in financing activities Increase in accured income taxes. Increase In Accured Income Taxes Increase in accured income taxes Entity Filer Category Entity Filer Category Balance Sheet Location [Domain] United states marketplace member. United States Marketplace [Member] U.S. Marketplace Income Tax Authority, Name [Domain] Income Tax Authority, Name Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Foreign currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Total Accrued Liabilities, Current [Abstract] Short-term investments Short-Term Investments Short-Term Investments, Total Asset Class [Axis] Asset Class Total other income, net Total other income, net Nonoperating Income (Expense) Other income (expense), net Unpaid purchases of property and equipment and capitalized hosting arrangements Capital Expenditures Incurred but Not yet Paid Liabilities Total liabilities Property, Plant and Equipment [Table] Schedule Of Property Plant And Equipment [Table] Payments to Acquire Short-Term Investments Purchases of short-term investments Purchases of short-term investments Equity, Attributable to Parent Ending balance Beginning balance Total stockholders’ equity Net (loss) income Net income attributable to CarGurus, Inc. Net loss Other income, net: Nonoperating Income (Expense) [Abstract] Contract with Customer, Asset, after Allowance for Credit Loss, Current Deferred contract costs Contract with Customer, Asset, after Allowance for Credit Loss, Current, Total Area of Land Area of land CO Incentive Units, Subject Units and noncontrolling interest Co Incentive Units Subject Units and Noncontrolling Interest [Member] Co incentive units subject units and noncontrolling interest. Statement of Financial Position [Abstract] Weighted Average Number of Shares Outstanding, Diluted Diluted Weighted-average number of shares of common stock used in computing net income per share attributable to common stockholders — diluted Impairment of Long-Lived Assets to be Disposed of Impairment of long-lived assets Credit Facility [Axis] Decrease in right-of-use asset Operating Lease, Right-of-Use Asset, Periodic Reduction Effective Income Tax Rate Reconciliation, Percent Effective income tax rate Effective Income Tax Rate Reconciliation, Percent, Total Use of Estimates, Policy [Policy Text Block] Use of Estimates Income Tax Disclosure [Text Block] Income Taxes Guarantees, description Guarantor Obligations, Term Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Schedule of Reconciliation of Numerator and Denominator Used in Calculation of Basic and Diluted Net Income Per Share Disaggregation of Revenue [Line Items] Leasehold Improvements [Member] Leasehold Improvements Income Tax Authority [Axis] Income Tax Authority Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items] Marketplace Marketplace [Member] Marketplace [Member] Fair Value Disclosures [Abstract] Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Consolidated comprehensive income Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV Measurement Frequency [Domain] Measurement Frequency Payments to Acquire Property, Plant, and Equipment Purchases of property and equipment Payments to Acquire Property, Plant, and Equipment, Total Business Acquisition [Axis] Business Acquisition Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations Cash, cash equivalents, and restricted cash at end of period Cash, cash equivalents, and restricted cash at beginning of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations, Total Tax distribution to redeemable noncontrolling interest holders Tax Distribution to Redeemable Noncontrolling Interest Holders Tax distribution to redeemable noncontrolling interest holders. Income Tax Disclosure [Abstract]