Entity Central Index Key Cover [Abstract] Document and entity information. Document and entity information Document And Entity Information [Table] Document And Entity Information [Table] Class of Stock Statement Class Of Stock [Axis] Class of Stock Class Of Stock [Domain] Class A Common Stock Common Class A [Member] Class B Common Stock Common Class B [Member] Document And Entity Information [Line Items] Document And Entity Information [Line Items] Document Type Document Type Amendment Flag Amendment Flag Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Entity Registrant Name Entity Registrant Name Trading Symbol Trading Symbol Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Small Business Entity Small Business Entity Emerging Growth Company Entity Emerging Growth Company Entity Common Stock, Shares Outstanding Entity Common Stock Shares Outstanding Entity Shell Company Entity Shell Company Entity Current Reporting Status Entity Current Reporting Status Entity File Number Entity File Number Entity Tax Identification Number Entity Tax Identification Number Entity Address, Address Line One Entity Address Address Line1 Entity Address, Address Line Two Entity Address Address Line2 Entity Address, City or Town Entity Address City Or Town Entity Address, State or Province Entity Address State Or Province Entity Address, Postal Zip Code Entity Address Postal Zip Code City Area Code City Area Code Local Phone Number Local Phone Number Entity Interactive Data Current Entity Interactive Data Current Document Quarterly Report Document Quarterly Report Document Transition Report Document Transition Report Entity Incorporation, State or Country Code Entity Incorporation State Country Code Title of 12(b) Security Security12b Title Security Exchange Name Security Exchange Name Liabilities convertible preferred stock and stockholders' deficit equity. Accrued liabilities accrued income taxes and other liabilities current. Statement Of Financial Position [Abstract] Statement [Table] Statement [Table] Statement [Line Items] Statement [Line Items] Assets Assets [Abstract] Current assets Assets Current [Abstract] Cash and cash equivalents Cash And Cash Equivalents At Carrying Value Investments Held To Maturity Securities Current Accounts receivable, net of allowance for doubtful accounts of $672 and $240, respectively Accounts Receivable Net Current Prepaid expenses and prepaid income taxes Prepaid Expense Current Deferred contract costs Contract With Customer Asset Net Current Other current assets Other Assets Current Restricted cash Restricted Cash Current Total current assets Assets Current Property and equipment, net Property Plant And Equipment Net Intangible assets Finite Lived Intangible Assets Net Goodwill Goodwill Operating lease right-of-use assets Operating Lease Right Of Use Asset Restricted cash Restricted Cash Noncurrent Deferred tax assets Deferred Income Tax Assets Net Deferred contract costs, net of current portion Contract With Customer Asset Net Noncurrent Other non-current assets Other Assets Noncurrent Total assets Assets Liabilities and stockholders’ equity Liabilities Convertible Preferred Stock And Stockholders Deficit Equity [Abstract] Current liabilities Liabilities Current [Abstract] Accounts payable Accounts Payable Current Accrued expenses, accrued income taxes and other current liabilities Accrued Liabilities Accrued Income Taxes And Other Liabilities Current Deferred revenue Contract With Customer Liability Current Operating lease liabilities Operating Lease Liability Current Total current liabilities Liabilities Current Operating lease liabilities Operating Lease Liability Noncurrent Deferred tax liabilities Deferred Income Tax Liabilities Net Other non–current liabilities Other Liabilities Noncurrent Total liabilities Liabilities Commitments and contingencies (Note 9) Commitments And Contingencies Stockholders’ equity: Stockholders Equity [Abstract] Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued and outstanding Preferred Stock Value Common stock Common Stock Value Additional paid-in capital Additional Paid In Capital Common Stock Retained earnings Retained Earnings Accumulated Deficit Accumulated other comprehensive loss Accumulated Other Comprehensive Income Loss Net Of Tax Total stockholders’ equity Stockholders Equity Total liabilities and stockholders’ equity Liabilities And Stockholders Equity Allowance for doubtful accounts Allowance For Doubtful Accounts Receivable Current Preferred stock, par value Preferred Stock Par Or Stated Value Per Share Preferred stock, shares authorized Preferred Stock Shares Authorized Preferred stock, shares issued Preferred Stock Shares Issued Preferred stock, shares outstanding Preferred Stock Shares Outstanding Common stock, par value Common Stock Par Or Stated Value Per Share Common stock, shares authorized Common Stock Shares Authorized Common stock, shares issued Common Stock Shares Issued Common stock, shares outstanding Common Stock Shares Outstanding Income Statement [Abstract] Revenue Revenue From Contract With Customer Excluding Assessed Tax Cost of revenue Cost Of Goods And Services Sold Gross profit Gross Profit Operating expenses: Operating Expenses [Abstract] Sales and marketing Selling And Marketing Expense Product, technology, and development Research And Development Expense General and administrative General And Administrative Expense Depreciation and amortization Depreciation And Amortization Total operating expenses Operating Expenses Income from operations Operating Income Loss Other income, net: Nonoperating Income Expense [Abstract] Interest income Investment Income Interest Other income, net Other Nonoperating Income Expense Total other income, net Nonoperating Income Expense Income before income taxes Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest Provision for (benefit from) income taxes Income Tax Expense Benefit Net income Net Income Loss Net income per share attributable to common stockholders: (Note 11) Earnings Per Share Basic And Diluted [Abstract] Basic Earnings Per Share Basic Diluted Earnings Per Share Diluted Weighted-average number of shares of common stock used in computing net income per share attributable to common stockholders: Weighted Average Number Of Shares Outstanding [Abstract] Basic Weighted Average Number Of Shares Outstanding Basic Diluted Weighted Average Number Of Diluted Shares Outstanding Depreciation and amortization expense Cost Of Goods And Services Sold Depreciation And Amortization Statement Of Income And Comprehensive Income [Abstract] Net income Other comprehensive income (loss): Other Comprehensive Income Loss Net Of Tax Period Increase Decrease [Abstract] Foreign currency translation adjustment Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Net Of Tax Comprehensive income Comprehensive Income Net Of Tax Convertible stock shares converted. Convertible stock converted value. Statement Of Stockholders Equity [Abstract] Accumulated Other Comprehensive (Loss) Income Statement Equity Components [Axis] Equity Component Equity Component [Domain] Common Stock Common Stock [Member] Additional Paid-in Capital Additional Paid In Capital [Member] Retained Earnings Retained Earnings [Member] Accumulated Other Comprehensive (Loss) Income Accumulated Other Comprehensive Income [Member] Beginning balance Beginning balance, Shares Stock–based compensation expense Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value Issuance of common stock upon exercise of stock options Stock Issued During Period Value Stock Options Exercised Issuance of common stock upon exercise of stock options, Shares Stock Issued During Period Shares Stock Options Exercised Issuance of common stock upon vesting of restricted stock units Stock Issued During Period Value Restricted Stock Award Net Of Forfeitures Issuance of common stock upon vesting of restricted stock units, Shares Stock Issued During Period Shares Restricted Stock Award Net Of Forfeitures Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options Adjustments Related To Tax Withholding For Share Based Compensation Payment of withholding taxes and option costs on net share settlement of restricted stock units and stock options, Shares Shares Paid For Tax Withholding For Share Based Compensation Conversion of common stock Stock Issued During Period Value Conversion Of Convertible Securities Net Of Adjustments Conversion of common stock, shares issued Stock Issued During Period Shares Conversion Of Convertible Securities Conversion of common stock, shares converted Convertible Stock Shares Converted Conversion of common stock, value Convertible Stock Converted Value Ending balance Ending balance, Shares Increase (decrease) in accrued liabilities accrued income taxes and other liabilities current. Increase decrease in lease obligations. Payment of withholding taxes on net share settlement of restricted stock units. Statement Of Cash Flows [Abstract] Operating Activities Net Cash Provided By Used In Operating Activities [Abstract] Net income Profit Loss Adjustments to reconcile net income to net cash provided by operating activities: Adjustments To Reconcile Net Income Loss To Cash Provided By Used In Operating Activities [Abstract] Depreciation and amortization Depreciation Depletion And Amortization Currency gain on foreign denominated transactions Foreign Currency Transaction Gain Loss Before Tax Deferred taxes Deferred Income Tax Expense Benefit Provision for doubtful accounts Provision For Doubtful Accounts Stock-based compensation expense Share Based Compensation Amortization of deferred contract costs Capitalized Contract Cost Amortization Changes in operating assets and liabilities: Increase Decrease In Operating Capital [Abstract] Accounts receivable, net Increase Decrease In Accounts Receivable Prepaid expenses, prepaid income taxes, and other assets Increase Decrease In Prepaid Deferred Expense And Other Assets Deferred contract costs Increase Decrease In Contract With Customer Asset Accounts payable Increase Decrease In Accounts Payable Accrued expenses, accrued income taxes, and other current liabilities Increase Decrease In Accrued Liabilities Accrued Income Taxes And Other Liabilities Current Deferred revenue Increase Decrease In Contract With Customer Liability Lease obligations Increase Decrease In Lease Obligations Other non-current liabilities Increase Decrease In Other Noncurrent Liabilities Net cash provided by operating activities Net Cash Provided By Used In Operating Activities Investing Activities Net Cash Provided By Used In Investing Activities [Abstract] Purchases of property and equipment Payments To Acquire Property Plant And Equipment Capitalization of website development costs Payments To Develop Software Cash paid for acquisition, net of cash acquired Payments To Acquire Businesses Net Of Cash Acquired Investments in certificates of deposit Payments To Acquire Restricted Certificates Of Deposit Maturities of certificates of deposit Proceeds From Sale Maturity And Collections Of Investments Net cash provided by (used in) investing activities Net Cash Provided By Used In Investing Activities Financing Activities Net Cash Provided By Used In Financing Activities [Abstract] Proceeds from exercise of stock options Proceeds From Stock Options Exercised Payment of finance lease obligations Finance Lease Principal Payments Payment of withholding taxes on net share settlement of restricted stock units Payment Of Withholding Taxes On Net Share Settlement Of Restricted Stock Units Net cash used in financing activities Net Cash Provided By Used In Financing Activities 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 Net increase (decrease) in cash, cash equivalents, and restricted cash Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect 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 Cash, cash equivalents, and restricted cash at end of period Supplemental disclosure of cash flow information: Supplemental Cash Flow Information [Abstract] Cash paid for income taxes Income Taxes Paid Unpaid purchases of property and equipment Capital Expenditures Incurred But Not Yet Paid Capitalized stock-based compensation expense in website development and internal-use software costs Employee Service Share Based Compensation Allocation Of Recognized Period Costs Capitalized Amount Cash paid for operating lease liabilities Operating Lease Payments Accounting Policies [Abstract] Organization and Business Description Organization Consolidation Basis Of Presentation Business Description And Accounting Policies [Text Block] Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Business Combinations [Abstract] Acquisitions Business Combination Disclosure [Text Block] Fair Value Disclosures [Abstract] Fair Value of Financial Instruments Including Cash, Cash Equivalents, and Investments Financial Instruments Disclosure [Text Block] Property Plant And Equipment [Abstract] Property and Equipment, Net Property Plant And Equipment Disclosure [Text Block] Goodwill And Intangible Assets Disclosure [Abstract] Goodwill and Other Intangible Assets Goodwill And Intangible Assets Disclosure [Text Block] Accrued Liabilities Current [Abstract] Accrued Expenses, Accrued Income Taxes and Other Current Liabilities Accounts Payable Accrued Liabilities And Other Liabilities Disclosure Current [Text Block] Restructuring And Related Activities [Abstract] Restructuring Restructuring And Related Activities Disclosure [Text Block] Commitments And Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments And Contingencies Disclosure [Text Block] Disclosure Of Compensation Related Costs Sharebased Payments [Abstract] Stock-based Compensation Disclosure Of Compensation Related Costs Share Based Payments [Text Block] Earnings Per Share [Abstract] Earnings Per Share Earnings Per Share [Text Block] Income Tax Disclosure [Abstract] Income Taxes Income Tax Disclosure [Text Block] Segment Reporting [Abstract] Segment and Geographic Information Segment Reporting Disclosure [Text Block] Basis of Presentation Basis Of Accounting Policy Policy [Text Block] Principles of Consolidation Consolidation Policy [Text Block] Subsequent Event Considerations Subsequent Events Policy Policy [Text Block] Use of Estimates Use Of Estimates Concentration of Credit Risk Concentration Risk Credit Risk Allowance for credit losses. Allowance for Credit Losses Allowance For Credit Losses Policy [Text Block] Revenue Recognition Revenue From Contract With Customer Policy [Text Block] Recent Accounting Pronouncements Adopted New Accounting Pronouncements Policy Policy [Text Block] Goodwill and Intangibles Goodwill And Intangible Assets Policy [Text Block] Credit Losses Credit Loss Financial Instrument Policy [Text Block] Recent accounting pronouncements not yet adopted. Recent Accounting Pronouncements not Yet Adopted Recent Accounting Pronouncements Not Yet Adopted Policy [Text Block] Income Taxes Income Tax Policy [Text Block] Fair Value of Financial Instruments Including Cash, Cash Equivalents, and Investments Fair Value Of Financial Instruments Policy Earnings Per Share Earnings Per Share Policy [Text Block] Summary of Changes in Allowance for Doubtful Accounts Accounts Receivable Allowance For Credit Loss Table [Text Block] Summary of Revenue from Contracts with Customers by Geographical Region and by Revenue Disaggregation Of Revenue Table [Text Block] Summary of Preliminary Purchase Price Allocation Schedule Of Recognized Identified Assets Acquired And Liabilities Assumed Table [Text Block] Schedule of Fair Value Levels, Assets Measured at Fair Value on Recurring Basis Fair Value Assets Measured On Recurring Basis [Text Block] Schedule of Investments Investment Table [Text Block] Schedule of Property and Equipment Property Plant And Equipment [Text Block] Summary of Changes in Carrying Value of Goodwill Schedule Of Goodwill [Text Block] Summary of Other Intangible Assets Schedule Of Finite Lived Intangible Assets Table [Text Block] Summary of Estimated Amortization Expense of Intangible Assets Scheduleof Finite Lived Intangible Assets Future Amortization Expense Table [Text Block] Schedule of accrued liabilities and other current liabilities. Schedule of Accrued Expenses, Accrued Income Taxes and Other Current Liabilities Schedule Of Accrued Liabilities And Other Current Liabilities Table [Text Block] Summary of Restructuring Accrual Activity for Employee Severance and Related Benefits Expense Schedule Of Restructuring Reserve By Type Of Cost [Text Block] Summary of Stock-based Compensation Expense by Award Type Schedule Of Compensation Cost For Share Based Payment Arrangements Allocation Of Share Based Compensation Costs By Plan Table [Text Block] Summary of Allocation of Stock-based Compensation Expense Schedule Of Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Text Block] Schedule of Reconciliation of Numerator and Denominator Used in Calculation of Basic and Diluted Net Income Per Share Schedule Of Earnings Per Share Basic And Diluted Table [Text Block] Schedule of Potentially Dilutive Common Stock Equivalents Excluded from Calculation of Diluted Weighted-average Shares Outstanding Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Text Block] Summary of Operations by Segment and Geographical Area Schedule Of Segment Reporting Information By Segment [Text Block] Organization Consolidation And Presentation Of Financial Statements [Abstract] State of incorporation Date of incorporation Entity Incorporation Date Of Incorporation Number of reportable segments Number Of Reportable Segments Summary of significant accounting policies. Summary of significant accounting policies. Summary Of Significant Accounting Policies [Table] Summary Of Significant Accounting Policies [Table] Concentration Risk Benchmark Concentration Risk By Benchmark [Axis] Concentration Risk Benchmark Concentration Risk Benchmark [Domain] Sales Revenue, Net Sales Revenue Net [Member] Concentration Risk Type Concentration Risk By Type [Axis] Concentration Risk Type Concentration Risk Type [Domain] Concentration of Credit Risk Customer Concentration Risk [Member] Customer Major Customers [Axis] Customer Name Of Major Customer [Domain] Customer one. Customer One Customer One [Member] Net Accounts Receivable Accounts Receivable [Member] Advertising customers. Advertising Customers Advertising Customers [Member] Geographical Statement Geographical [Axis] Geographical Segment Geographical [Domain] United States UNITED STATES Canada CANADA United Kingdom UNITED KINGDOM Italy ITALY Summary Of Significant Accounting Policies [Line Items] Summary Of Significant Accounting Policies [Line Items] Description of significant off-balance sheet risk Concentration Risk Credit Risk Financial Instruments Off Balance Sheet Risk Number of major customers. Concentration of credit risk, percentage Concentration Risk Percentage1 Number of major customers Number Of Major Customers Unbilled accounts receivable Unbilled Receivables Current Bad debt expense Allowance for doubtful accounts write offs, net Allowance For Doubtful Accounts Receivable Write Offs Balance at Beginning of Period Allowance For Doubtful Accounts Receivable Write–offs, Net of Recoveries Balance at End of Period Disaggregation Of Revenue [Table] Disaggregation Of Revenue [Table] International Non Us [Member] Product and Service Product Or Service [Axis] Product and Service Products And Services [Domain] Marketplace subscription revenue. Marketplace Subscription Revenue Marketplace Subscription Revenue [Member] Advertising and other revenue. Advertising and Other Revenue Advertising And Other Revenue [Member] Disaggregation Of Revenue [Line Items] Disaggregation Of Revenue [Line Items] Performance obligation unsatisfied Revenue Remaining Performance Obligation Revenue recognized Contract With Customer Liability Revenue Recognized Percentage fee reduction on marketplace subscription services. Percentage fee reduction on marketplace subscription services Percentage Fee Reduction On Marketplace Subscription Services Schedule Of Business Acquisitions By Acquisition [Table] Schedule Of Business Acquisitions By Acquisition [Table] Business Acquisition Business Acquisition [Axis] Business Acquisition, Acquiree Business Acquisition Acquiree [Domain] Auto List, Inc. Autolist, Inc Auto List Inc [Member] San Francisco, California CALIFORNIA Income Statement Location Income Statement Location [Axis] Income Statement Location Income Statement Location [Domain] Product, Technology, and Development Research And Development Expense [Member] General and Administrative General And Administrative Expense [Member] Sales and Marketing Selling And Marketing Expense [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Business acquisition date Business Acquisition Effective Date Of Acquisition1 Payments to acquire business Payments To Acquire Businesses Gross Amount held in escrow Escrow Deposit Acquisition-related costs incurred Business Acquisition Cost Of Acquired Entity Transaction Costs Acquisition-related costs incurred Business Combination Acquisition Related Costs Business combination recognized identifiable assets acquired and liabilities assumed restricted cash. Business combination recognized identifiable assets acquired and liabilities assumed operating lease right of use assets. Business combination recognized identifiable assets acquired and liabilities assumed accounts payable and accrued expenses. Business combination recognized identifiable assets acquired and liabilities assumed operating lease liabilities current. Business combination recognized identifiable assets acquired and liabilities assumed operating lease liabilities long term. Business combination recognized identifiable assets acquired and liabilities assumed deferred tax liability. Cash and cash equivalents Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Cash And Equivalents Restricted cash Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Restricted Cash Accounts receivable Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Current Assets Receivables Intangible assets Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Intangibles Operating lease right-of-use assets Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Operating Lease Right Of Use Assets Other assets, net Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Other Noncurrent Assets Accounts payable and accrued expenses Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Accounts Payable And Accrued Expenses Operating lease liabilities - current Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Operating Lease Liabilities Current Operating lease liabilities - non-current Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Operating Lease Liabilities Long Term Deferred tax liabilities Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Deferred Tax Liability Total purchase price Business Combination Recognized Identifiable Assets Acquired Goodwill And Liabilities Assumed Net Finite-Lived Intangible Assets by Major Class Finite Lived Intangible Assets By Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name Finite Lived Intangible Assets Major Class Name [Domain] Brand. Brand Brand [Member] Developed Technology Developed Technology Rights [Member] Customer Relationships Customer Relationships [Member] Intangible assets Estimated useful lives Finite Lived Intangible Asset Useful Life Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table] Measurement Frequency Fair Value By Measurement Frequency [Axis] Measurement Frequency Fair Value Measurement Frequency [Domain] Fair Value, Measurements, Recurring Fair Value Measurements Recurring [Member] Asset Class Fair Value By Asset Class [Axis] Asset Class Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation By Asset Class [Domain] Money Market Funds Money Market Funds [Member] Fair Value Hierarchy and NAV Fair Value By Fair Value Hierarchy Level [Axis] Fair Value Hierarchy and NAV Fair Value Measurements Fair Value Hierarchy [Domain] Quoted Prices in Active Markets for Identical Assets (Level 1 Inputs) Fair Value Inputs Level1 [Member] Significant Other Observable Inputs (Level 2 Inputs) Fair Value Inputs Level2 [Member] Significant Unobservable Inputs (Level 3 Inputs) Fair Value Inputs Level3 [Member] 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] Cash equivalents: Cash And Cash Equivalents Fair Value Disclosure Investments: Debt Securities, Held-to-maturity, Type [Extensible List] Debt Securities Held To Maturity Type Extensible List Total Assets Fair Value Disclosure Maturity period of certificates of deposit Maturity Of Time Deposits Maturity of certificates of deposit, description Maturities Of Time Deposits Description Liabilities, fair value Liabilities Fair Value Disclosure Held to maturity amortized cost. Certificates of deposit due in one year or less, Amortized Cost Total investments, Amortized Cost Held To Maturity Amortized Cost Held to maturity fair value. Certificates of deposit due in one year or less, Estimated Fair Value Held To Maturity Securities Fair Value Total investments, Estimated Fair Value Held To Maturity Fair Value Schedule Of Property Plant And Equipment [Table] Schedule Of Property Plant And Equipment [Table] Long-Lived Tangible Asset Property Plant And Equipment By Type [Axis] Long-Lived Tangible Asset Property Plant And Equipment Type [Domain] Computer Equipment Computer Equipment [Member] Capitalized Software Software And Software Development Costs [Member] Capitalized Website Development Costs Software Development [Member] Furniture and Fixtures Furniture And Fixtures [Member] Leasehold Improvements Leasehold Improvements [Member] Construction in Progress Construction In Progress [Member] Finance lease right-of-use assets. Finance Lease Right-of-use Assets Finance Lease Right Of Use Assets [Member] Property Plant And Equipment [Line Items] Property Plant And Equipment [Line Items] Property and equipment, gross Property Plant And Equipment Gross Less accumulated depreciation and amortization Accumulated Depreciation Depletion And Amortization Property Plant And Equipment Property and equipment, net Depreciation Depreciation Balance at December 31, 2019 Autolist acquisition Goodwill Acquired During Period Foreign currency translation adjustment Goodwill Foreign Currency Translation Gain Loss Balance at June 30, 2020 Schedule Of Goodwill [Table] Schedule Of Goodwill [Table] PistonHeads Holdco Limited. PistonHeads Piston Heads Holdco Limited [Member] Autolist Goodwill [Line Items] Goodwill [Line Items] Impairment of goodwill as a result of COVID-19 Goodwill Impairment Loss Schedule Of Finite Lived Intangible Assets [Table] Schedule Of Finite Lived Intangible Assets [Table] Finite Lived Intangible Assets [Line Items] Finite Lived Intangible Assets [Line Items] Weighted Average Remaining Useful Life (years) Acquired Finite Lived Intangible Assets Weighted Average Useful Life Gross Carrying Amount Finite Lived Intangible Assets Gross Accumulated Amortization Finite Lived Intangible Assets Accumulated Amortization Net Carrying Amount Amortization expense of intangible assets Amortization Of Intangible Assets Estimated useful life Impairment of intangible assets, finite-lived as a result of COVID-19 Impairment Of Intangible Assets Finitelived Remainder of 2020 Finite Lived Intangible Assets Amortization Expense Remainder Of Fiscal Year 2021 Finite Lived Intangible Assets Amortization Expense Next Twelve Months 2022 Finite Lived Intangible Assets Amortization Expense Year Two 2023 Finite Lived Intangible Assets Amortization Expense Year Three 2024 Finite Lived Intangible Assets Amortization Expense Year Four 2025 Finite Lived Intangible Assets Amortization Expense Year Five Thereafter Finite Lived Intangible Assets Amortization Expense After Year Five Other accrued expenses, accrued income taxes and other liabilities Accrued bonus Accrued Bonuses Current Other accrued expenses, accrued income taxes and other current liabilities Other Accrued Expenses Accrued Income Taxes And Other Liabilities Total Decrease in accrued bonus. Decrease in accrued bonus Decrease In Accrued Bonus Schedule Of Restructuring And Related Costs [Table] Schedule Of Restructuring And Related Costs [Table] Restructuring Plan Restructuring Plan [Axis] Restructuring Plan Restructuring Plan [Domain] Expense deduction plan. Expense Reduction Plan Expense Reduction Plan [Member] Restructuring Type Restructuring Cost And Reserve [Axis] Type of Restructuring Type Of Restructuring [Domain] Employee Severance and Related Benefits Expense Employee Severance [Member] Product, technology, and development. Product, Technology, and Development Product Technology And Development [Member] Cost of Revenue Cost Of Sales [Member] Stock based compensation expense. Stock-Based Compensation Expense Stock Based Compensation Expense [Member] Cost of Revenue Sales and Marketing Restructuring Cost And Reserve [Line Items] Restructuring Cost And Reserve [Line Items] Workforce reduction, percent Restructuring And Related Cost Number Of Positions Eliminated Period Percent Write-off of capitalized website development costs and deferred contract costs. Restructuring and related charges Restructuring Charges Write-off of capitalized website development costs and deferred contract costs Write Off Of Capitalized Website Development Costs And Deferred Contract Costs Balance, April 1, 2020 Restructuring Reserve Charges Cash disbursements Payments For Restructuring Noncash settlements Restructuring Reserve Settled Without Cash2 Balance, June 30, 2020 Write-off of capitalized website development costs. Write-off of deferred contract costs. Write-off of capitalized website development costs Write Off Of Capitalized Website Development Costs Write-off of deferred contract costs Write Off Of Deferred Contract Costs Commitments and contingencies. Commitments and contingencies. Commitments And Contingencies [Table] Commitments And Contingencies [Table] Boston, Massachusetts one zero zero one Boylston. Boston, Massachusetts at 1001 Boylston St Boston Massachusetts One Zero Zero One Boylston [Member] San Francisco California three three two pine street. San Francisco, California at 332 Pine St San Francisco California Three Three Two Pine Street [Member] Commitments And Contingencies [Line Items] Commitments And Contingencies [Line Items] Operating lease, office space Land Subject To Ground Leases Restricted cash Restricted Cash Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table] Schedule Of Share Based Compensation Arrangements By Share Based Payment Award [Table] Award Type Award Type [Axis] Award Type Share Based Compensation Arrangements By Share Based Payment Award Award Type And Plan Name [Domain] Stock Options Employee Stock Option [Member] Restricted Stock Units Restricted Stock Units R S U [Member] Share Based Compensation Arrangement By Share Based Payment Award [Line Items] Share Based Compensation Arrangement By Share Based Payment Award [Line Items] Total stock-based compensation expense Allocated Share Based Compensation Expense Schedule Of Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Table] Schedule Of Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Table] Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] 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 Employee tax withholding requirements due to net share settlement Total payments for employees' tax obligations to taxing authorities due to net share settlements Number of votes entitled to stockholders per share. Undistributed earnings ratio used to calculate allocation to class of stock. Schedule Of Earnings Per Share Basic By Common Class [Table] Schedule Of Earnings Per Share Basic By Common Class [Table] Earnings Per Share Basic [Line Items] Earnings Per Share Basic [Line Items] Right to voting Common Stock Voting Rights Number of votes entitled to stockholders per share Number Of Votes Entitled To Stockholders Per Share Conversion of stock, description Conversion Of Stock Description Class of share converted to another class Conversion Of Stock Type Of Stock Converted Conversion of stock Conversion Of Stock Shares Issued1 Undistributed earnings ratio used to calculate allocation to class of stock Undistributed Earnings Ratio Used To Calculate Allocation To Class Of Stock Numerator: Net Income Loss [Abstract] Denominator: Weighted-average number of shares of common stock used in computing net income per share attributable to common stockholders — basic Dilutive effect of share equivalents resulting from stock options Incremental Common Shares Attributable To Share Based Payment Arrangements Dilutive effect of share equivalents resulting from unvested restricted stock units Incremental Common Shares Attributable To Equity Unit Purchase Agreements Weighted-average number of shares of common stock used in computing net income per share — diluted Net income per share attributable to common stockholders: Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table] Schedule Of Antidilutive Securities Excluded From Computation Of Earnings Per Share [Table] Antidilutive Securities Antidilutive Securities Excluded From Computation Of Earnings Per Share By Antidilutive Securities [Axis] Antidilutive Securities, Name Antidilutive Securities Name [Domain] Restricted Stock Units Outstanding Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items] 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 Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount Income tax provision (benefit) Effective income tax rate Effective Income Tax Rate Continuing Operations Statutory tax rate Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate CARES Act of twenty twenty reduction in gross net operating loss (NOL) current. CARES Act of twenty twenty increase in deferred federal research & development credit. Reduction in gross net operating loss current C A R E S Act Of Twenty Twenty Decrease In Gross Net Operating Loss Current Increase in deferred federal research & development credit C A R E S Act Of Twenty Twenty Increase In Deferred Federal Research Development Credit CARES Act of twenty twenty limitation on net operating loss to offset taxable income. Limitation on net operating loss to offset taxable income C A R E S Act Of Twenty Twenty Limitation On Net Operating Loss To Offset Taxable Income Schedule Of Segment Reporting Information By Segment [Table] Schedule Of Segment Reporting Information By Segment [Table] United States Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Segment revenue: Segment Reporting Information Revenue [Abstract] Segment income (loss) from operations: Segment Reporting Information Operating Income Loss [Abstract] Total income from operations Assets Employee severance and related benefits expense