Deferred tax assets Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets Supplemental cash flow disclosures: Supplemental Cash Flow Information [Abstract] Foreign currency transaction gain (loss), realized Foreign Currency Transaction Gain (Loss), Realized Letter of Credit Letter of Credit [Member] Net Income Per Share Earnings Per Share, Policy [Policy Text Block] Restricted Cash and Cash Equivalents [Axis] Restricted Cash and Cash Equivalents [Axis] Vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period State Current State and Local Tax Expense (Benefit) Leasehold improvements Leasehold Improvements [Member] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy and NAV [Domain] Net income Net income Net income Net Income (Loss) Attributable to Parent Lease right-of-use assets Operating Lease, Right-of-Use Asset Net operating losses Deferred Tax Assets, Operating Loss Carryforwards Net income per share - basic (usd per share) Business Acquisition, Pro Forma Earnings Per Share, Basic Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Depreciated assets written-off Fully Depreciated Assets, Write-Off Fully Depreciated Assets, Write-Off Accrued wages and commissions Employee-related Liabilities, Current Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs, by Report Line [Axis] Income Statement Location [Axis] Income Statement Location [Axis] Accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization GOODWILL Goodwill Disclosure [Text Block] Statistical Measurement [Domain] Statistical Measurement [Domain] Other intangible assets Other Intangible Assets [Member] Acquired Technology Acquired Technology [Member] Acquired Technology [Member] Schedule of Maturities of Long-term Debt Schedule of Maturities of Long-term Debt [Table Text Block] Aircrafts Aircraft [Member] Aircraft [Member] Discounted rate par value Debt Instrument, Par Value, Discounted Rate Debt Instrument, Par Value, Discounted Rate Security Exchange Name Security Exchange Name Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Canceled (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] 48.82 Exercise Range 2 [Member] The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices. Contract With Customer, Asset and Liability Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block] Impairment of intangible assets Impairment of Intangible Assets (Excluding Goodwill) Numerator: Earnings Per Share Reconciliation [Abstract] New deferrals, net of amounts recognized in the current period Contract with Customer, Liability, New Deferrals, Net of Amounts Recognized in Current Period Contract with Customer, Liability, New Deferrals, Net of Amounts Recognized in Current Period Weighted-average remaining lease term in years Operating Lease, Weighted Average Remaining Lease Term Foreign Currency Translation Foreign Currency Transactions and Translations Policy [Policy Text Block] Granted (dollars per share) Sharebased Compensation Shares Granted Under Stock Option Plans Exercise Price Range The range of exercise prices for purposes of disclosing stock option granted and other required information pertaining to stock option plans in the customized range. Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Shares available for future grant under the plan (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Net increase (decrease) in cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Acquired Finite-Lived Intangible Assets [Line Items] Acquired Finite-Lived Intangible Assets [Line Items] Deferred commission costs, net Deferred Costs, Noncurrent Entity File Number Entity File Number Redemption price rate Debt Instrument, Redemption Price, Percentage Expected volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Common stock Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract] 2023 Long-Term Debt, Maturity, Year Two Stock-based compensation expense APIC, Share-based Payment Arrangement, Increase for Cost Recognition Income taxes payable Increase (Decrease) in Income Taxes Payable Aggregate intrinsic value of options exercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Canceled or expired (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period Accumulated Other Comprehensive Income (Loss) Net of Tax [Abstract] Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] Range of exercise price, minimum, (in dollars per share) Share-based Payment Arrangement, Option, Exercise Price Range, Lower Range Limit Charged to expense SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Cost and Expense Cash paid for amounts included in the measurement of lease liabilities: Cash Paid For Amounts Included In Measurement Of Lease Liabilities [Abstract] Cash Paid For Amounts Included In Measurement Of Lease Liabilities [Abstract] Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] New deferrals recognized in connection with business acquisitions made in 2021 Deferred tax liabilities, net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Customer base amortization Amortization of Intangible Assets Long-term debt principal payments Maturities of Long-term Debt [Abstract] Intangible assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill Weighted- Average Amortization Period (in years) Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Increase for prior year tax positions Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions Antidilutive securities excluded from computation of earnings per share (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Weighted-average discount rate Operating Lease, Weighted Average Discount Rate, Percent Sale of Stock [Axis] Sale of Stock [Axis] Deferred commission costs, net Deferred Tax Liabilities, Accrued Commissions Deferred Tax Liabilities, Accrued Commissions Commitment fees and other Line of Credit Facility, Commitment Fee Amount Buildings Building [Member] Current-period provision (release) for expected credit losses Financing Receivable, Credit Loss, Expense (Reversal) Total deferred tax assets, net of valuation allowance Deferred Tax Assets, Net of Valuation Allowance Business Combination and Asset Acquisition [Abstract] Conversion ratio Stockholders' Equity Note, Stock Split, Conversion Ratio Weighted-average grant date fair value (in dollars per share) Granted (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Commitment fee percentage Line of Credit Facility, Commitment Fee Percentage Business Acquisition [Axis] Business Acquisition [Axis] Purchase price, net of estimated working capital adjustments Business Combination, Consideration Transferred, Net of Adjustments Business Combination, Consideration Transferred, Net of Adjustments Title of Individual [Domain] Title of Individual [Domain] Unrealized gain on investments OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax Award Type [Domain] Award Type [Domain] Exercise Price Range [Axis] Exercise Price Range [Axis] Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract] Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract] Accrual amount Business Combination, Accrual Amount Business Combination, Accrual Amount Local Phone Number Local Phone Number Credit Facility [Domain] Credit Facility [Domain] ASSETS Assets [Abstract] Exercisable at end of period (dollars per share) Exercisable at end of period The range of exercise prices for purposes of disclosing stock option exercisable at the end of the period and other required information pertaining to stock option plans in the customized range. Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] 2024 Long-Term Debt, Maturity, Year Three Exercisable at end of period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Operating Loss Carryforwards [Line Items] Operating Loss Carryforwards [Line Items] Land Land [Member] Long-Lived Assets, Intangible Assets and Goodwill Goodwill and Intangible Assets, Policy [Policy Text Block] Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Cash Equivalents Cash Equivalents [Member] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Preferred stock, $0.01 par value; 2,000 shares authorized; zero outstanding Preferred Stock, Value, Issued Acquisitions, including measurement period adjustments Goodwill, Acquisitions and Adjustments Goodwill, Acquisitions and Adjustments Estimated Fair Value Finite-lived Intangible Assets Acquired Property and Equipment, Net Property, Plant and Equipment, Policy [Policy Text Block] Administrative expense Defined Contribution Plan, Administrative Expense New Accounting Pronouncements or Change in Accounting Principle [Table] Accounting Standards Update and Change in Accounting Principle [Table] Schedule of Commissions Expense Schedule of Commissions Expense [Table Text Block] Schedule of Commissions Expense [Table Text Block] Outstanding at beginning of period (in shares) Outstanding at end of period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Trade name Acquired trade names and other intangible assets Trade Names [Member] Retained Earnings Retained Earnings [Member] Debt Instrument [Axis] Debt Instrument [Axis] Prepaid expenses and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Debt outstanding, fair value Debt Instrument, Fair Value Disclosure Advertising Costs Advertising Cost [Policy Text Block] COMMITMENTS AND CONTINGENCIES Commitments and Contingencies Disclosure [Text Block] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Leases, Operating [Abstract] Leases, Operating [Abstract] Accounts receivable Increase (Decrease) in Accounts Receivable Operating leases Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Business Acquisition, Pro Forma Information Business Acquisition, Pro Forma Information [Table Text Block] Schedule of Deferred Tax Assets and Liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Term of subscription-based license agreements Subscription-Based Licensing Agreement Minimum Term Years Subscription-Based Licensing Agreement Minimum Term Years Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Share-based compensation arrangement, award vesting rights, percentage Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] MSPP RSUs MSPP RSUs [Member] MSPP RSUs [Member] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Deferred revenue Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Deferred Revenue Restricted stock grants surrendered Adjustments to Additional Paid in Capital, Restricted Stock Surrendered Adjustments to Additional Paid in Capital, Restricted Stock Surrendered Number of business segments Number of operating segments Number of Operating Segments Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] Net income per share — basic (in dollars per share) Earnings Per Share, Basic 2024 Lessee, Operating Lease, Liability, to be Paid, Year Three REVENUE FROM CONTRACTS WITH CUSTOMERS Revenue from Contract with Customer [Text Block] Allowance for Credit Losses Credit Loss, Financial Instrument [Policy Text Block] Outstanding (dollars per share) Outstanding (dollars per share) Sharebased Compensation Shares Outstanding Under Stock Option Plans Exercise Price Range The minimum and maximum exercise price range as of the balance sheet date at which grantees could acquire the underlying shares with respect to all outstanding stock options which are in the customized range of exercise prices. Homesnap Homesnap [Member] Homesnap Unvested restricted stock at beginning of period (in shares) Unvested restricted stock at end of period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Total leverage ratio Line Of Credit Facility, Covenant Compliance, Total Leverage Ratio Line Of Credit Facility, Covenant Compliance, Total Leverage Ratio 2022 Long-Term Debt, Maturity, Year One Fair value of identifiable net assets acquired Fair value of identifiable net assets acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net Total interest expense Interest Expense, Debt Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] 2026 Long-Term Debt, Maturity, Year Five Company match to employee contributions Defined Contribution Plan, Cost Number of Shares(1) Weighted-Average Grant Date Fair Value per Share(1) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Increase in shares of common stock issued pursuant to stock plan (in shares) Increase In Shares Of Common Stock Issued Pursuant To Stock Plan The increase in the number of shares of common stock for issuance under the company stock plan. Schedule II - Valuation and Qualifying Accounts SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block] Homes.com Homes.com [Member] Homes.com Research and development credits Deferred Tax Assets, Tax Credit Carryforwards Tax reserves Effective Income Tax Rate Reconciliation, Change In Tax Reserves, Amount Effective Income Tax Rate Reconciliation, Change In Tax Reserves, Amount Cumulative Effect, Period of Adoption, Adjustment Cumulative Effect, Period of Adoption, Adjustment [Member] Thereafter Long-Term Debt, Maturity, Interest Payments, After Year Five Long-Term Debt, Maturity, Interest Payments, After Year Five Shares of common stock authorized for issuance under the plan (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Net deferred tax assets (liabilities) Deferred Tax Liabilities, Net Operating cash flows used in operating leases Operating Lease, Payments Revolving Loans and Letters of Credit Revolving Loans and Letters of Credit [Member] Revolving Loans and Letters of Credit Performance-based restricted stock awards Performance Based Restricted Stock [Member] Performance Based Restricted Stock [Member] Property and equipment, net Deferred Tax Liabilities, Property, Plant and Equipment ROU assets obtained in exchange for lease obligations: Right Of Use Assets Obtained In Exchange For Lease Obligations [Abstract] Right Of Use Assets Obtained In Exchange For Lease Obligations [Abstract] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Aggregate purchase price Business Combination, Consideration Transferred Depreciation and other amortization Other Depreciation and Amortization Credit loss expense Accounts Receivable, Credit Loss Expense (Reversal) Increase in revenue Increase in Revenue Increase in Revenue Non-cash lease expense Non Cash Lease Expense Non Cash Lease Expense Goodwill [Roll Forward] Goodwill [Roll Forward] Entity Voluntary Filers Entity Voluntary Filers Canceled or expired (dollars per share) Sharebased Compensation Shares Canceled or Expired Under Stock Option Plans Exercise Price Range The range of exercise prices for purposes of disclosing stock option canceled or expired and other required information pertaining to stock option plans in the customized range. Plan Name [Axis] Plan Name [Axis] Total Long-term Debt LoopNet LoopNet [Member] LoopNet Financing Receivable Portfolio Segment [Axis] Financing Receivable Portfolio Segment [Axis] Total assets measured at fair value Assets, Fair Value Disclosure Lease right-of-use assets Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Finance Lease, Right-Of-Use Asset Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Finance Lease, Right-Of-Use Asset Fair Value, Inputs, Level 1 Fair Value, Inputs, Level 1 [Member] Investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Unrecognized Tax Benefits [Roll Forward] Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] Goodwill, impairment Goodwill, Impairment Loss Other operating activities, net Other Operating Activities, Cash Flow Statement Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] State income taxes, net of federal benefit Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount Software development Software development Software Development [Member] Small Business Entity Entity Small Business Operating lease obligations Lessee, Operating Lease, Liability, Payment, Due [Abstract] Schedule of Financing Receivable, Allowance for Credit Loss Financing Receivable, Allowance for Credit Loss [Table Text Block] Increase for current year tax positions Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions Finite-Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets [Line Items] Total liabilities and stockholders’ equity Liabilities and Equity Accrued compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation Purchases of property and equipment and other assets Payments to Acquire Property and Equipment and Other Assets Payments to Acquire Property and Equipment and Other Assets Goodwill increase (decrease) Goodwill, Period Increase (Decrease) Cost of revenues Cost of Revenues [Member] Cost of Revenues [Member] Deferred revenue Current liability Contract with Customer, Liability, Current 2026 Lessee, Operating Lease, Liability, to be Paid, Year Five DSU DSU [Member] DSU Exercised (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Restricted cash Restricted Cash Amortization of deferred commissions costs Amortization of deferred commissions costs Amortization of Deferred Sales Commissions Additional paid-in capital Additional Paid in Capital Weighted-Average Grant Date Fair Value per Share(1) Number of Matching RSU Shares(1) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] LIABILITIES AND STOCKHOLDERS’ EQUITY Liabilities and Equity [Abstract] Unrecognized tax benefits that would favorably affect the annual effective tax rate if recognized in future periods Unrecognized Tax Benefits that Would Impact Effective Tax Rate Residential Residential [Member] Residential Weighted-average exercise price (in dollars per share) Share-based Payment Arrangement, Option, Exercise Price Range, Exercisable, Weighted Average Exercise Price SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table] NET INCOME PER SHARE Earnings Per Share [Text Block] Operating expenses: Operating Expenses [Abstract] Entity Interactive Data Current Entity Interactive Data Current Foreign Plan Foreign Plan [Member] Thereafter Long-Term Debt, Maturity, after Year Five Amortization expense for 2024 Finite-Lived Intangible Asset, Expected Amortization, Year Four Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Decrease for settlements with taxing authorities Decrease for settlements with taxing authorities Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities Exercise of stock options Stock Issued During Period, Value, Stock Options Exercised Minimum Minimum [Member] Summarized Information by Operating Segment, Assets and Liabilities Reconciliation of Assets from Segment to Consolidated [Table Text Block] Gross profit Gross Profit 2023 Lessee, Operating Lease, Liability, to be Paid, Year Two Effect of foreign currency exchange rates on cash and cash equivalents Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Balance Sheet Location [Domain] Balance Sheet Location [Domain] Percentage of purchase price of company's common stock to the market price Percentage of purchase price of company's common stock to the market price The percentage of market price that eligible employees under the plan can purchase company stock. Canceled or expired (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price Debt issuance costs, net Debt Issuance Costs, Net Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Reduction to allowance for credit loss, adjustment Allowance for Loan and Lease Losses, Adjustments, Other Preferred stock, shares authorized (in shares) Preferred stock authorized for issuance (in shares) Preferred Stock, Shares Authorized  Options Exercisable Options Exercisable [Abstract] Unrecognized tax benefits beginning balance Unrecognized tax benefits ending balance Unrecognized Tax Benefits Income Tax Authority [Domain] Income Tax Authority [Domain] Total deferred tax assets, prior to valuation allowance Deferred Tax Assets, Gross Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Address, State or Province Entity Address, State or Province Cumulative Effect, Period of Adoption [Axis] Cumulative Effect, Period of Adoption [Axis] Proceeds from sale of property and equipment and other assets Proceeds From Sale Of Property And Equipment And Other Assets Proceeds From Sale Of Property And Equipment And Other Assets Alternate Base Rate Alternate Base Rate [Member] Alternate Base Rate Write-offs charged against the allowance, net of recoveries and other Financing Receivable, Allowance for Credit Loss, Writeoff, after Recovery Deferred income taxes, net Deferred Income Tax Assets, Net Current liabilities: Liabilities, Current [Abstract] 2025 Long-Term Debt, Maturity, Year Four Stock issued for equity offerings, net of transaction costs/Stock issued for acquisitions Stock Issued During Period, Value, New Issues General and administrative General and Administrative Expense Revision of Prior Period [Axis] Revision of Prior Period [Axis] Cash paid for acquisitions, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Balance (in shares) Balance (in shares) Shares, Outstanding Exercisable at end of period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price Schedule of Components of Income Tax Expense Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] Restricted stock issued Stock Issued During Period, Value, Restricted Stock Award, Gross Number of shares (in shares) Share-based Payment Arrangement, Option, Exercise Price Range, Shares Exercisable EMPLOYEE BENEFIT PLANS Share-based Payment Arrangement [Text Block] Leases Lessee, Leases [Policy Text Block] Registered Retirement Savings Plan Supplemental Employee Retirement Plan [Member] ALLOWANCE FOR CREDIT LOSSES Credit Loss, Financial Instrument [Text Block] Interest and penalties accrued on income taxes Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued Lease right-of-use assets Deferred Tax Liabilities, Lease Right of Use Assets Deferred Tax Liabilities, Lease Right of Use Assets Accounting Policies [Abstract] Accounting Policies [Abstract] Weighted average remaining contract life, outstanding Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Payments of stock issuance costs Payments of Stock Issuance Costs Stock issued for equity offerings, net of transaction costs/Stock issued for acquisitions (in shares) Stock Issued During Period, Shares, New Issues Ten-X Ten-X [Member] Ten-X Retirement Plan Sponsor Location [Axis] Retirement Plan Sponsor Location [Axis] Federal Current Federal Tax Expense (Benefit) Present value of lease liabilities Operating Lease, Liability Document Transition Report Document Transition Report Common stock, $0.01 par value; 1.2 billion shares authorized; 394,936 and 394,285 issued and outstanding as of December 31, 2021 and 2020, respectively Common Stock, Value, Issued Indemnification asset Business Combination, Indemnification Assets, Range of Outcomes, Value, High Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Accrued reserve and other Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Reserves Weighted-average-period expected to recognize the unrecognized compensation cost (in years) Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Unvested restricted stock at beginning of period (in dollars per share) Unvested restricted stock at end of period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Goodwill acquired Goodwill acquired Goodwill, Acquired During Period Performance Shares Performance-based RSAs - with Market Condition Performance Shares [Member] LEASES Lessee, Operating Leases [Text Block] Number of portfolio segments Number of Portfolio Segments Number of Portfolio Segments Accumulated other comprehensive loss Total accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Consideration owed for acquisitions Other Significant Noncash Transaction, Amounts Owed for Acquisitions Other Significant Noncash Transaction, Amounts Owed for Acquisitions Emerging Growth Entity Emerging Growth Company Less: Allowance for credit losses Accounts Receivable, Allowance for Credit Loss, Current Income taxes payable Accrued Income Taxes, Noncurrent ACQUISITIONS Business Combination Disclosure [Text Block] Restricted Stock Restricted Stock [Member] Contract with customer, asset, gross Contract with Customer, Asset, before Allowance for Credit Loss Payments of debt issuance costs Payments of Debt Issuance Costs ICFR Auditor Attestation Flag ICFR Auditor Attestation Flag Fair Value Assumption for Options Granted Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Amortization period of deferred sales commissions Deferred Sales Commission, Amortization Period Deferred Sales Commission, Amortization Period Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Foreign Deferred Foreign Income Tax Expense (Benefit) INVESTMENTS AND FAIR VALUE MEASUREMENTS Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Auditor Name Auditor Name Cover [Abstract] Cover [Abstract] Stock options, restricted stock awards and restricted stock units (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Goodwill [Line Items] Goodwill [Line Items] Software development Research and Development Expense, Software (Excluding Acquired in Process Cost) Shares available, employee stock purchase plan (in shares) Shares Available, Employee Stock Purchase Plan Number of shares available as a result of an employee stock purchase plan. 91.98 Exercise Range 4 [Member] The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices. Net income Business Acquisition, Pro Forma Net Income (Loss) Cumulative Effect, Period of Adoption, Adjusted Balance Cumulative Effect, Period of Adoption, Adjusted Balance [Member] RentPath break fee held in escrow under the terms of the Asset Purchase Agreement RentPath Break Fee [Member] RentPath Break Fee Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Financing Receivable, Allowance for Credit Loss [Roll Forward] Financing Receivable, Allowance for Credit Loss [Roll Forward] Less: imputed interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Ten-X, Homesnap and STR Ten-X, Homesnap and STR [Member] Ten-X, Homesnap and STR Subsidiary or Equity Method Investee, Sale of Stock by Subsidiary or Equity Investee [Table] Subsidiary or Equity Method Investee, Sale of Stock by Subsidiary or Equity Investee [Table] Consideration received on transaction Sale of Stock, Consideration Received on Transaction Income Tax Authority [Axis] Income Tax Authority [Axis] 24.24 Exercise Range 1 [Member] The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices. Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Financial Instrument [Axis] Financial Instrument [Axis] Borrowings Borrowings [Member] Accrued expenses Accrued Liabilities, Current Revenues Revenue from Contract with Customer, Excluding Assessed Tax Stock compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost Weighted-average remaining contractual life (in years) Share-based Payment Arrangement, Option, Exercise Price Range, Outstanding, Weighted Average Remaining Contractual Term Lease liabilities Increase (Decrease) In Lease Liability Increase (Decrease) In Lease Liability Current: Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Stock Options Share-based Payment Arrangement, Option [Member] Consolidation Items [Domain] Consolidation Items [Domain] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Accrued capital expenditures and non-cash landlord incentives Capital Expenditures Incurred but Not yet Paid and Noncash Landlord Incentives Capital Expenditures Incurred but Not yet Paid and Noncash Landlord Incentives Operating Loss Carryforwards [Table] Operating Loss Carryforwards [Table] Common Stock Common Stock [Member] Variable Rate [Axis] Variable Rate [Axis] Indefinite-lived intangible assets, written off Indefinite-lived Intangible Assets, Written off Indefinite-lived Intangible Assets, Written off Income from foreign sources Income (Loss) from Continuing Operations before Income Taxes, Foreign SEGMENT REPORTING Segment Reporting Disclosure [Text Block] Income from operations Operating Income (Loss) Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Revenue recognized in the current period from the amounts in the beginning balance Contract with Customer, Liability, Prior Period Amounts Recognized Contract with Customer, Liability, Prior Period Amounts Recognized Lease liabilities Operating Lease, Liability, Current SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Amortization expense for 2022 Finite-Lived Intangible Asset, Expected Amortization, Year Two Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Document Fiscal Year Focus Document Fiscal Year Focus Foreign currency translation adjustment Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax Cash tax benefits resulting in net operating loss carryforward Realized Tax Benefits Related To Operating Loss Carryforward Amount of cash benefit realized from tax operating losses. An unrecognized tax benefit is presented in the financial statements as a reduction to a deferred tax asset. except as follows. To the extent a operating loss carryforward is not available at the reporting date under the tax law of the applicable jurisdiction to settle any additional income taxes that would result from the disallowance of a tax position, the unrecognized tax benefit is be presented in the financial statements as a liability and is not be combined with deferred tax assets. Acquired customer base Customer Contracts [Member] Property, Plant and Equipment [Abstract] Property, Plant and Equipment [Abstract] Stock-based compensation expense Share-based Payment Arrangement, Noncash Expense Variable Rate [Domain] Variable Rate [Domain] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Additional Paid-in Capital Additional Paid-in Capital [Member] Depreciation expense for property and equipment Depreciation Schedule of Acquired Finite-Lived Intangible Asset by Major Class [Table] Schedule of Acquired Finite-Lived Intangible Asset by Major Class [Table] Technology Technology-Based Intangible Assets [Member] Cash and Cash Equivalents [Abstract] Cash and Cash Equivalents [Abstract] Previously Reported Previously Reported [Member] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Unvested Restricted Stock Awards Activity Share-based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block] Supplemental Balance Sheet Information Related to Leases Supplemental Balance Sheet Information Related to Leases [Table Text Block] Supplemental Balance Sheet Information Related to Leases [Table Text Block] Income taxes paid Income Taxes Paid Other Assets Other Assets [Member] Other income (expense), net Other income (expense), net Other Nonoperating Income (Expense) Credit Loss [Abstract] Purchase of Richmond assets and other intangibles Payments to Acquire Property, Plant, and Equipment Proceeds from exercise of stock options and employee stock purchase plan Proceeds From Exercise Of Stock Options and ESPP The cash inflow associated with the amount received from holders exercising their stock options and participants of employee stock purchase plans. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately. Maximum Maximum [Member] Effective tax rate reconciliation [Abstract] Effective Income Tax Rate Reconciliation, Percent [Abstract] Stock-Based Compensation Expense [Abstract] Share-based Payment Arrangement [Abstract] Total liabilities                                                                                                     Total liabilities Liabilities Intangible Assets, Net (Excluding Goodwill) [Abstract] Intangible Assets, Net (Excluding Goodwill) [Abstract] Award Type [Axis] Award Type [Axis] Amortization expense for 2021 Finite-Lived Intangible Asset, Expected Amortization, Year One Number of classes of trade receivables based on location Number of Classes of Trade Receivables Based on Location Number of Classes of Trade Receivables Based on Location Granted (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Income tax receivable Income Taxes Receivable, Noncurrent Aggregate intrinsic value of options outstanding at end of period Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Expense related to stock options settled Share-based Payment Arrangement, Expensed and Capitalized, Amount Lessee, Operating Lease, Liability, Maturity Lessee, Operating Lease, Liability, Maturity [Table Text Block] Consolidation Items [Axis] Consolidation Items [Axis] Total stockholders’ equity Balance Balance Stockholders' Equity Attributable to Parent Net operating loss carryforward Operating Loss Carryforwards Common stock, shares issued, (in shares) Common Stock, Shares, Issued City Area Code City Area Code Preferred stock Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract] Financing Receivable, Allowance for Credit Loss [Table] Financing Receivable, Allowance for Credit Loss [Table] Accounts payable and other liabilities Increase (Decrease) in Accounts Payable and Accrued Liabilities Aggregate intrinsic value of options exercisable at end of period Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Decrease in net income Decrease in Net Income Decrease in Net Income Goodwill and Intangible Assets Disclosure [Abstract] Goodwill and Intangible Assets Disclosure [Abstract] Entity Address, City or Town Entity Address, City or Town Number of Allowable Increase Requests Number of Allowable Increase Requests Number of Allowable Increase Requests INTANGIBLE ASSETS Intangible Assets Disclosure [Text Block] 2026 Long-Term Debt, Maturity, Interest Payments, Year Five Long-Term Debt, Maturity, Interest Payments, Year Five Useful life Property, Plant and Equipment, Useful Life Schedule of Accumulated Other Comprehensive Loss Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Schedule of Unrecognized Tax Benefits Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block] Number of trade receivables in information services portfolio Number of Trade Receivables in Information Services Portfolio Number of Trade Receivables in Information Services Portfolio Concentration of Credit Risk Concentration Risk, Credit Risk, Policy [Policy Text Block] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Long-term lease liabilities Operating Lease, Liability, Noncurrent Total current Current Income Tax Expense (Benefit) Total face amount of long-term debt Debt Instrument, Face Amount Deferred: Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract] Cash Reconciliation [Table] Cash Reconciliation [Table] Cash Reconciliation [Table] International restructuring Effective Income Tax Rate Reconciliation, Nondeductible Expense, Restructuring Charges, Amount Tax benefit from stock-based compensation Share-based Payment Arrangement, Expense, Tax Benefit Retained earnings Retained Earnings (Accumulated Deficit) Operating Segments Operating Segments [Member] Term of contract Lessee, Operating Lease, Term of Contract Restricted Stock Units (RSUs) Restricted Stock Units (RSUs) [Member] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Revision of Prior Period [Domain] Revision of Prior Period [Domain] Schedule of Recognized Identified Assets Acquired and Liabilities Assumed Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Employee stock purchase plan (in shares) Shares of company's common stock purchased during the period (in shares) Stock Issued During Period, Shares, Employee Stock Purchase Plans Entity Filer Category Entity Filer Category Lease and other long-term liabilities Lease and Other Liabilities, Noncurrent Lease and Other Liabilities, Noncurrent Maximum percentage of employee total compensation matched by employer (in hundredths) Defined Contribution Plan, Employer Matching Contribution, Percent of Match Total deferred tax liabilities Deferred Tax Liabilities, Gross Business Acquisition [Line Items] Business Acquisition [Line Items] Risk-free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Purchase price due Business Combinations, Purchase Price, Term Business Combinations, Purchase Price, Term Restrictions on Cash and Cash Equivalents Restrictions on Cash and Cash Equivalents [Table Text Block] Income Statement [Abstract] Income Statement [Abstract] Entity Registrant Name Entity Registrant Name Net income per share - diluted (usd per share) Business Acquisition, Pro Forma Earnings Per Share, Diluted Accounts receivable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables Commissions capitalized in the current period Commissions Capitalized in the Current Period Commissions Capitalized in the Current Period Write-offs, net of recoveries SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction Weighted- average exercise price (in dollars per share) Share-based Payment Arrangement, Option, Exercise Price Range, Outstanding, Weighted Average Exercise Price Restricted stock issued (in shares) Stock Issued During Period, Shares, Restricted Stock Award, Gross Other adjustments Effective Income Tax Rate Reconciliation, Other Adjustments, Amount Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Income tax expense Income tax expense Income Tax Expense (Benefit) Accounts receivable, net Accounts Receivable, after Allowance for Credit Loss, Current Amendment Flag Amendment Flag Proceeds from long-term debt Proceeds from Issuance of Long-term Debt Equity Components [Axis] Equity Components [Axis] Entity Tax Identification Number Entity Tax Identification Number SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] 2020 Credit Agreement 2020 Credit Agreement [Member] 2020 Credit Agreement Antidilutive Securities Excluded from Computation of Earnings Per Share, by Antidilutive Securities [Axis] Antidilutive Securities [Axis] Document Fiscal Period Focus Document Fiscal Period Focus CoStar Group, Inc. 2007 Stock Incentive Plan CoStar Group, Inc. 2007 Stock Incentive Plan [Member] Employee stock incentive plan name. Total current assets Assets, Current Summarized Information Regarding Options Outstanding Share-based Payment Arrangement, Option, Exercise Price Range [Table Text Block] Change in Contract with Customer, Liability [Roll Forward] Change in Contract with Customer, Liability [Roll Forward] Change in Contract with Customer, Liability [Roll Forward] Selling and marketing (excluding customer base amortization) Selling and marketing (excluding customer base amortization) Selling and Marketing Expense [Member] Sale of Stock [Domain] Sale of Stock [Domain] Total Lessee, Operating Lease, Liability, to be Paid Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Canceled (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Denominator: Weighted Average Number of Shares Outstanding Reconciliation [Abstract] 2022 Long-Term Debt, Maturity, Interest Payments, Year One Long-Term Debt, Maturity, Interest Payments, Year One Reclassification adjustment for realized loss on investments included in net income Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures Summarized EBITDA Information by Operating Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] (Decrease) in valuation allowance Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount Stock-Based Compensation Share-based Payment Arrangement [Policy Text Block] Federal Deferred Federal Income Tax Expense (Benefit) Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Thereafter Lessee, Operating Lease, Liability, to be Paid, after Year Five SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract] SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract] 69.93 Exercise Range 3 [Member] The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices. Decrease in valuation allowance Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount Product and Service [Axis] Product and Service [Axis] Property, Plant and Equipment, Type [Domain] Long-Lived Tangible Asset [Domain] Nondeductible compensation Effective Income Tax Rate Reconciliation, Nondeductible Expense, Compensation, Amount Effective Income Tax Rate Reconciliation, Nondeductible Expense, Compensation, Amount Schedule of Cash and Cash Equivalents Schedule of Cash and Cash Equivalents [Table Text Block] Preferred stock, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Public Float Entity Public Float Documents Incorporated by Reference Documents Incorporated by Reference [Text Block] Weighted-average grant date fair value (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Equity Component [Domain] Equity Component [Domain] Financing Receivable, Allowance for Credit Loss [Line Items] Financing Receivable, Allowance for Credit Loss [Line Items] Prepaid expenses Deferred Tax Liabilities, Prepaid Expenses BureauxLocaux BureauxLocaux [Member] BureauxLocaux Other Marketplaces Other Marketplaces [Member] Other Marketplaces Selling and marketing (excluding customer base amortization) Selling and Marketing Expense 2022 Lessee, Operating Lease, Liability, to be Paid, Year One Commissions incurred Commissions Incurred Commissions Incurred Foreign currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Furniture and office equipment Furniture And Office Equipment [Member] Furniture And Office Equipment 2023 Long-Term Debt, Maturity, Interest Payments, Year Two Long-Term Debt, Maturity, Interest Payments, Year Two Vehicles Vehicles [Member] Statement [Line Items] Statement [Line Items] Restricted stock grants surrendered (in shares) Stock Issued During Period, Shares, Restricted Stock Award, Forfeited Deferred revenue Increase (Decrease) in Contract with Customer, Liability Remaining performance obligation Revenue, Remaining Performance Obligation, Amount Retirement Plan Type [Domain] Retirement Plan Type [Domain] Domestic Country Domestic Tax Authority [Member] Emporis Emporis [Member] Emporis Proceeds from sale and settlement of investments Proceeds from Sale, Maturity and Collection of Investments 2025 Lessee, Operating Lease, Liability, to be Paid, Year Four Debt Disclosure [Abstract] Debt Disclosure [Abstract] Board of Directors Board of Directors [Member] Board of Directors Finite-Lived Intangible Assets Acquired as Part of Business Combination [Table] Finite-Lived Intangible Assets Acquired as Part of Business Combination [Table] Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Fair Value, Inputs, Level 2 Fair Value, Inputs, Level 2 [Member] Research credits Effective Income Tax Rate Reconciliation, Tax Credit, Research, Amount Property, Plant and Equipment, Type [Axis] Long-Lived Tangible Asset [Axis] Subsidiary, Sale of Stock [Line Items] Subsidiary, Sale of Stock [Line Items] Valuation allowance Deferred Tax Assets, Valuation Allowance Noncurrent liability Contract with Customer, Liability, Noncurrent Auditor Location Auditor Location Dividends common stock, shares (in shares) Dividends Common Stock, Shares Dividends Common Stock, Shares Investments And Fair Value Disclosures [Abstract] Investments And Fair Value Disclosures Segment Reporting [Abstract] Segment Reporting [Abstract] Exercised (dollars per share) Sharebased Compensation Shares Exercised Under Stock Option Plans Exercise Price Range The range of exercise prices for purposes of disclosing stock option exercised and other required information pertaining to stock option plans in the customized range. Useful life Estimated Useful Life Finite-Lived Intangible Asset, Useful Life Use of Estimates Use of Estimates, Policy [Policy Text Block] Calculation of Basic and Diluted Net Income (Loss) Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Document Annual Report Document Annual Report Schedule of Stock-Based Compensation Expense for Stock Options and Restricted Stock Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Title of 12(b) Security Title of 12(b) Security Proceeds from equity offering, net of transaction costs Proceeds from Issuance of Common Stock Total assets Total assets Assets Revision of Prior Period, Adjustment Revision of Prior Period, Adjustment [Member] Plan Name [Domain] Plan Name [Domain] Common stock, shares authorized (in shares) Common stock authorized for issuance (in shares) Common Stock, Shares Authorized Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activities Geographical [Domain] Geographical [Domain] Title of Individual [Axis] Title of Individual [Axis] Document Type Document Type CoStar Group, Inc. 2016 Stock Incentive Plan CoStar Group, Inc. 2016 Stock Incentive Plan [Member] CoStar Group, Inc. 2016 Stock Incentive Plan [Member] Product and Service [Domain] Product and Service [Domain] Stated interest rate Debt Instrument, Interest Rate, Stated Percentage Financing Receivable Portfolio Segment [Domain] Financing Receivable Portfolio Segment [Domain] Reclassification out of accumulated other comprehensive loss Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Deferred Tax Assets, Accrued Transaction Fees Deferred Tax Assets, Accrued Transaction Fees Deferred Tax Assets, Accrued Transaction Fees Revenue, remaining performance obligation, expected timing of satisfaction, period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Cumulative Effect, Period of Adoption [Domain] Cumulative Effect, Period of Adoption [Domain] Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Total Long-Term Debt, Maturity, Interest Payments Long-Term Debt, Maturity, Interest Payments Income tax credit carryforward Tax Credit Carryforward, Amount Furniture, office equipment and vehicles Furniture and Fixtures [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Table] Fair Value, Recurring and Nonrecurring [Table] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Components of Lease Expense Lease, Cost [Table Text Block] Goodwill [Abstract] Goodwill [Abstract] Geographical [Axis] Geographical [Axis] Weighted average outstanding shares — basic (in shares) Denominator for basic net income per share — weighted-average outstanding shares Weighted Average Number of Shares Outstanding, Basic Net income per share — diluted (in dollars per share) Earnings Per Share, Diluted State and Local Jurisdiction State and Local Jurisdiction [Member] Amortization of senior notes discount and issuance costs Amortization of Debt Issuance Costs and Discounts Sale of stock, price per share (usd per share) Sale of Stock, Price Per Share Term of credit facility Line of Credit Facility, Expiration Period Cash Reconciliation [Line Items] Cash Reconciliation [Line Items] Cash Reconciliation International Non-US [Member] Intangible assets, net Intangible Assets, Net (Excluding Goodwill) Total comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent CoStar CoStar Suite [Member] CoStar Suite [Member] Beginning balance Ending balance Contract with Customer, Liability Goodwill, expected tax deductible amount Business Acquisition, Goodwill, Expected Tax Deductible Amount Schedule of Interest Expense Schedule of Interest Expense [Table Text Block] Schedule of Interest Expense Net cash (used in) provided by financing activities Net Cash Provided by (Used in) Financing Activities Aircrafts Aircrafts [Member] Aircrafts Other comprehensive (loss) income, net of tax Other Comprehensive Income (Loss), Net of Tax [Abstract] Debt Issuance Costs Debt, Policy [Policy Text Block] Deferred income taxes, net Deferred Income Tax Liabilities, Net Vesting period of options and restricted stock grants Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Schedule of Supplemental Cash Flow Information for Leases Schedule of Supplemental Cash Flow Information for Leases [Table Text Block] Schedule of Supplemental Cash Flow Information for Leases [Table Text Block] Income tax penalties and interest expense (reversal) Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Schedule of Effective Income Tax Rate Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] INVESTMENTS AND FAIR VALUE MEASUREMENTS Fair Value Disclosures [Text Block] Commitments and Contingencies Liability Reserve Estimate, Policy [Policy Text Block] Accounts payable Accounts Payable, Current Allowance for credit losses Deferred Tax Asset, Tax Deferred Expense, Reserve and Accrual, Accounts Receivable, Allowance for Credit Loss Depreciation and amortization Depreciation, Depletion and Amortization Amortization expense for 2023 Finite-Lived Intangible Asset, Expected Amortization, Year Three Foreign Country Foreign Tax Authority [Member] Deferred tax liabilities: Deferred Tax Liabilities, Gross [Abstract] Business Combinations Business Combinations Policy [Policy Text Block] Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Financial Instruments [Domain] Financial Instruments [Domain] Cost of revenues Cost of Goods and Services Sold Document Period End Date Document Period End Date Entity Central Index Key Entity Central Index Key Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Share Based Compensation Exercisable Range [Abstract] Share Based Compensation Exercisable Range [Abstract] Share Based Compensation Exercisable Range [Abstract] Amortization of acquired intangible assets in cost of revenues Amortization Of Intangible Assets, Cost of Revenue Amortization Of Intangible Assets, Cost of Revenue Deferred tax assets: Deferred Tax Assets, Gross [Abstract] State Deferred State and Local Income Tax Expense (Benefit) Schedule of Property and Equipment Property, Plant and Equipment [Table Text Block] Other assets Increase (Decrease) Lease Right of Use and Other Assets Increase (Decrease) Lease Right of Use and Other Assets Long-term debt principal interest payments Long-Term Debt, Maturity, Interest Payments [Abstract] Long-Term Debt, Maturity, Interest Payments Income Statement Location [Domain] Income Statement Location [Domain] Range of exercise price, maximum, (in dollars per share) Share-based Payment Arrangement, Option, Exercise Price Range, Upper Range Limit Stockholders’ equity: Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Decrease for prior year tax positions Decrease for prior year tax positions Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions Supplemental non-cash investing and financing activities: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Customer base Customer Relationships [Member] Number of trade receivables in multifamily portfolio Number of Trade Receivables in Multifamily Portfolio Number of Trade Receivables in Multifamily Portfolio Compensation Related Costs [Abstract] Compensation Related Costs [Abstract] Transaction costs Business Acquisition, Transaction Costs Property and equipment, net Property and equipment, net Property, Plant and Equipment, Net PROPERTY AND EQUIPMENT Property, Plant and Equipment Disclosure [Text Block] Total operating expenses Operating Expenses Schedule of Long-term Debt Instruments Schedule of Long-term Debt Instruments [Table Text Block] Debt Instrument [Line Items] Debt Instrument [Line Items] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table] Payments of long-term debt Repayments of Long-term Debt Trading Symbol Trading Symbol Earnings Per Share [Abstract] Earnings Per Share [Abstract] Purchase price before adjustments Business Combination, Acquisition Price Before Working Capital and Other Adjustments Business Combination, Acquisition Price Before Working Capital and Other Adjustments Public Offering Public Offering [Member] Public Offering Revenue Business Acquisition, Pro Forma Revenue Property and equipment, gross Property, Plant and Equipment, Gross Lease liabilities Deferred Tax Assets, Lease Liabilities Deferred Tax Assets, Lease Liabilities Computer hardware and software Computer Hardware And Software [Member] Computer Hardware And Software Deferred stock unit, granted percentage Deferred Stock Unit, Granted Percentage Deferred Stock Unit, Granted Percentage Reclassification from accumulated other comprehensive income, current period, net of tax Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Management stock purchase plan APIC, Share-based Payment Arrangement, Management Plan APIC, Share-based Payment Arrangement, Management Plan Total EBITDA EBITDA Net income (loss) before interest and other income (expense), income taxes, depreciation and amortization (“EBITDA”) Net income (loss) before interest and other income (expense), income taxes, depreciation and amortization (“EBITDA”) Multifamily Multifamily Online Marketplace [Member] Multifamily Online Marketplace [Member] Outstanding at beginning of period (in dollars per share) Outstanding at end of period (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List] Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Long-term debt, net Long-term debt, net Long-term Debt, Excluding Current Maturities Schedule of Goodwill [Table] Schedule of Goodwill [Table] Compensation expense Share-based Payment Arrangement, Expense Cost of Revenues Cost of Goods and Service [Policy Text Block] Weighted average remaining contract life, outstanding, exercisable Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Entity Current Reporting Status Entity Current Reporting Status Excess tax benefit Effective Income Tax Rate Reconciliation, Excess Tax Benefit, Amount Effective Income Tax Rate Reconciliation, Excess Tax Benefit, Amount Performance Based RSAs Without Market Condition Performance Based RSAs Without Market Condition [Member] Performance Based RSAs Without Market Condition [Member] Defined Contribution Plan Disclosure [Line Items] Defined Contribution Plan Disclosure [Line Items] Accounts receivable Accounts Receivable, before Allowance for Credit Loss, Current Amortization of debt issuance costs Amortization of Debt Issuance Costs 2025 Long-Term Debt, Maturity, Interest Payments, Year Four Long-Term Debt, Maturity, Interest Payments, Year Four Cash, cash equivalents and restricted cash Cash, cash equivalents and restricted cash at beginning of year Cash, cash equivalents and restricted cash at end of year Cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Number of shares issued in transaction (in shares) Sale of Stock, Number of Shares Issued in Transaction Common stock, par or stated value per share (in dollars per share) Common Stock, Par or Stated Value Per Share Deferred sales commissions of impaired Deferred Sales Commissions, Impairment Deferred Sales Commissions, Impairment Current assets: Assets, Current [Abstract] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Other financing activities Proceeds from (Payments for) Other Financing Activities Finite-lived intangible assets, gross Finite-Lived Intangible Assets, Gross Interest (expense) income, net Interest expense (income), net Interest Income (Expense), Nonoperating, Net Leases [Abstract] Leases [Abstract] Income Taxes Income Tax, Policy [Policy Text Block] London Interbank Offered Rate (LIBOR) London Interbank Offered Rate (LIBOR) [Member] Entity Address, Postal Zip Code Entity Address, Postal Zip Code STR STR [Member] STR Revenue Recognition Revenue from Contract with Customer [Policy Text Block] Exercise of stock options (in shares) Exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Other assets and liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Assets And Liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Assets And Liabilities Weighted average outstanding shares — diluted (in shares) Denominator for diluted net income per share — weighted-average outstanding shares (in shares) Weighted Average Number of Shares Outstanding, Diluted Income from U.S. sources Income (Loss) from Continuing Operations before Income Taxes, Domestic Exercise Price Range [Domain] Exercise Price Range [Domain] Total other comprehensive (loss) income Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax Amortization of intangible assets Amortization Performance service period Share-based Compensation Arrangement by Share-based Payment Award, Award Requisite Service Period INCOME TAXES Income Tax Disclosure [Text Block] Schedule of Option Activity Share-based Payment Arrangement, Option, Activity [Table Text Block] Schedule of Acquired Finite-Lived Intangible Assets by Major Class Schedule of Acquired Finite-Lived Intangible Assets by Major Class [Table Text Block] Total commissions expense Sales Commissions and Fees Basis spread Debt Instrument, Basis Spread on Variable Rate  Options Outstanding Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract] STOCKHOLDERS' EQUITY Stockholders' Equity Note Disclosure [Text Block] Expiration of the statute of limitation for assessment of taxes Expiration of the statute of limitation for assessment of taxes Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations 2.800% Senior Notes 2.800 Senior Notes [Member] 2.800 Senior Notes Schedule of Anti-Dilutive Securities Excluded From Computation of Earnings Per Share Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Amortization expense for 2025 Finite-Lived Intangible Asset, Expected Amortization, Year Five Financial Instruments Fair Value of Financial Instruments, Policy [Policy Text Block] Performance-based RSAs - with Market Condition Performance-based RSAs - with Market Condition [Member] Shares or units awarded to employees for meeting certain performance and market targets. Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Auditor Firm ID Auditor Firm ID Lease liabilities Business Combination, Recognized Identifiable Asset Acquired and Liability Assumed, Lease Obligation Credit Facility [Axis] Credit Facility [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Entity Address, Address Line One Entity Address, Address Line One Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Reconciliation of Net Income to EBITDA Reconciliation of Operating Profit (Loss) from Segments to Consolidated [Table Text Block] Changes in operating assets and liabilities, net of acquisitions: Increase (Decrease) in Operating Capital [Abstract] Retirement Plan Sponsor Location [Domain] Retirement Plan Sponsor Location [Domain] Accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Employee stock purchase plan Stock Issued During Period, Value, Employee Stock Purchase Plan Operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Vested (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Total deferred Deferred Other Tax Expense (Benefit) General and administrative General and administrative General and Administrative Expense [Member] Basis of Presentation Consolidation, Policy [Policy Text Block] Entity Shell Company Entity Shell Company Amortization of acquired intangible assets in operating expenses Amortization Of Intangible Assets, Net Of Adjustments Amortization Of Intangible Assets, Net Of Adjustments Expected life (in years) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Total current liabilities Liabilities, Current Repurchase of restricted stock to satisfy tax withholding obligations Payment, Tax Withholding, Share-based Payment Arrangement Intangible assets, net Deferred Tax Liabilities, Goodwill and Intangible Assets Effects of foreign currency Contract with Customer, Asset, Effects of Currency Translation Contract with Customer, Asset, Effects of Currency Translation Revolving credit sub-facility for swing-line loans and issuances of letters of credit Maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Effect of foreign currency translation Goodwill, Foreign Currency Translation Gain (Loss) Cash, cash equivalents and restricted cash Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Schedule of Finite-Lived Intangible Assets Acquired as Part of Business Combination Schedule of Finite-Lived Intangible Assets Acquired as Part of Business Combination [Table Text Block] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Current Fiscal Year End Date Current Fiscal Year End Date Senior notes unamortized discount and issuance costs Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Statement [Table] Statement [Table] Advertising costs Advertising Expense Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Effect of dilutive securities: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] Compensation cost expected to be recognized in future years Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Information services Information Services [Member] Information services [Member] Statistical Measurement [Axis] Statistical Measurement [Axis] Expected federal income tax provision at statutory rate Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount North America North America [Member] Management Stock Purchase Plan Management Stock Purchase Plan [Member] Management Stock Purchase Plan [Member] 2024 Long-Term Debt, Maturity, Interest Payments, Year Three Long-Term Debt, Maturity, Interest Payments, Year Three Deposits and other assets Deposits Assets, Noncurrent Stockholders' Equity Note [Abstract] Stockholders' Equity Note [Abstract] Beginning balance at December 31, 2020 Ending balance at December 31, 2021 Financing Receivable, Allowance for Credit Loss Finite-lived intangible assets, net Finite-Lived Intangible Assets, Net Other restricted cash related to acquisitions Other, Related to Acquisition [Member] Other, Related to Acquisition Goodwill Goodwill, beginning balance Goodwill, ending balance Goodwill Deferred commissions Increase (Decrease) Deferred Commissions Increase (Decrease) Deferred Commissions Number of shares (in shares) Share-based Payment Arrangement, Option, Exercise Price Range, Shares Outstanding Balance at beginning of year Balance at end of year SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount Cost of revenues                                                                                        Cost of Sales [Member] Income taxes payable Accrued Income Taxes, Current Foreign Current Foreign Tax Expense (Benefit) Schedule of Goodwill Schedule of Goodwill [Table Text Block] ORGANIZATION Nature of Operations [Text Block] 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] Pension Plan Pension Plan [Member] Acquired technology and data Developed Technology Rights [Member] Audit Information [Abstract] Audit Information Operating lease costs: Operating Lease, Cost Computer hardware and software Computer Equipment [Member] Maximum annual employee contribution Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] LONG-TERM DEBT Long-term Debt [Text Block] Deferred income taxes, net Deferred Income Tax Expense (Benefit)