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of Components of Income Tax Expense Schedule of Components of Income Tax Expense (Benefit) [Table Text Block] DSU DSU [Member] DSU OnTheMarket OnTheMarket [Member] OnTheMarket Entity File Number Entity File Number Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Operating Loss Carryforwards [Line Items] Operating Loss Carryforwards [Line Items] Thereafter Lessee, Operating Lease, Liability, to be Paid, after Year Five Less: current portion of lease liabilities Operating Lease, Liability, Current Unvested Restricted Stock Awards Activity Share-Based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block] 2026 Long-Term Debt, Maturity, Year Three Interest on lease liabilities Finance Lease, Interest Expense Residential Residential [Member] Residential 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 Decrease for prior year tax positions Decrease for prior year tax positions Unrecognized Tax Benefits, Decrease Resulting from Prior Period Tax Positions Auditor Firm ID Auditor Firm ID Customer base amortization Amortization of Intangible Assets Entity Shell Company Entity Shell Company 2026 Lessee, Operating Lease, Liability, to be Paid, Year Three Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Finite-lived intangible assets, net Finite-Lived Intangible Assets, Net Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Recently Adopted and Not Yet Adopted Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Income taxes payable, net Increase (Decrease) in Income Taxes Payable Increase for current year tax positions Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions Financing Receivable, Allowance for Credit Loss [Table] Financing Receivable, Allowance for Credit Loss [Table] Cash and cash equivalents Cash and cash equivalents at beginning of year Cash and cash equivalents at end of year Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents Accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization $66.98 - $91.98 Exercise Range 5 [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. 2025 Lessee, Operating Lease, Liability, to be Paid, Year Two Debt outstanding, fair value Debt Instrument, Fair Value Disclosure Sale of stock, price per share (usd per share) Sale of Stock, Price Per Share Income from foreign sources Income (Loss) from Continuing Operations before Income Taxes, Foreign Denominator: Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Total operating lease costs Operating Lease, Cost 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. 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$66.97 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. 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] Expected federal income tax provision at statutory rate Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount Long-term debt principal payments Maturities of Long-Term Debt [Abstract] Entity Tax Identification Number Entity Tax Identification Number Effect of foreign currency translation Goodwill, Foreign Currency Translation Gain (Loss) Total lease costs Lease, Cost Land Land [Member] Statistical Measurement [Axis] Statistical Measurement [Axis] $20.49 - $27.35 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. Balance Sheet Location [Domain] Balance Sheet Location [Domain] Financial Instrument [Axis] Financial Instrument [Axis] Acquired customer base Customer Contracts [Member] Entity Interactive Data Current Entity Interactive Data Current Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] LONG-TERM DEBT Long-Term Debt [Text Block] Advertising Costs Advertising Cost [Policy Text Block] Interest on outstanding borrowings Borrowings [Member] Number of shares (in shares) Share-Based Payment Arrangement, Option, Exercise Price Range, Shares Exercisable Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Long-Lived Assets, Intangible Assets and Goodwill Goodwill and Intangible Assets, Policy [Policy Text Block] Lease liabilities Increase (Decrease) In Lease Liability Increase (Decrease) In Lease Liability Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Foreign Deferred Foreign Income Tax Expense (Benefit) Supplemental non-cash investing and financing activities: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Other Assets Other Assets [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Retained earnings Retained Earnings (Accumulated Deficit) Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Restricted stock issued (in shares) Stock Issued During Period, Shares, Restricted Stock Award, Gross Revenue Recognition Revenue from Contract with Customer [Policy Text Block] 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 Exercise Price Range [Axis] Exercise Price Range [Axis] Intangible assets, net Deferred Tax Liabilities, Goodwill and Intangible Assets Total face amount of long-term debt Debt Instrument, Face Amount Indefinite-lived intangible assets, written off Indefinite-lived Intangible Assets, Written off Indefinite-lived Intangible Assets, Written off Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Current assets: Assets, Current [Abstract] Leases [Abstract] Leases [Abstract] Accounts receivable Accounts Receivable, before Allowance for Credit Loss, Current Advertising costs Advertising Expense 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 Schedule of Deferred Tax Assets and Liabilities Schedule of Deferred Tax Assets and Liabilities [Table Text Block] Entity Address, State or Province Entity Address, State or Province Finance lease liabilities Finance Lease, Liability, to be Paid Operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] 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. Amortization expense for 2024 Finite-Lived Intangible Asset, Expected Amortization, Year One Operating cash flows used in operating leases Operating Lease, Payments Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Impairment loss Operating Lease, Impairment Loss Commitments and Contingencies Liability Reserve Estimate, Policy [Policy Text Block] Number of trade receivables in loopnet portfolio Number of Trade Receivables in LoopNet Portfolio Number of Trade Receivables in LoopNet Portfolio Concentration of Credit Risk and Financial Instruments Concentration Risk, Credit Risk, Policy [Policy Text Block] Auditor Location Auditor Location Adjustment to SOFR Adjustment to SOFR [Member] Adjustment to SOFR Cash Equivalents Cash Equivalents [Member] 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] Other operating activities, net Other Operating Activities, Cash Flow Statement Beginning balance (in shares) Ending balance (in shares) Shares, Outstanding Defined Contribution Plan Disclosure [Line Items] Defined Contribution Plan Disclosure [Line Items] State income taxes, net of federal benefit Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount Common stock, par or stated value per share (in dollars per share) Common Stock, Par or Stated Value Per Share Maximum annual employee contribution Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent Sale of Stock [Axis] Sale of Stock [Axis] Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities 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. 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] Debt Instrument [Axis] Debt Instrument [Axis] Deferred tax liabilities: Deferred Tax Liabilities, Gross [Abstract] Present value of lease liabilities Operating Lease, Liability Credit Facility [Axis] Credit Facility [Axis] 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 Schedule of Maturities of Long-term Debt Schedule of Maturities of Long-Term Debt [Table Text Block] Total liabilities Total liabilities Liabilities Total current Current Income Tax Expense (Benefit) Expected volatility Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Volatility Rate Asset Acquisition [Axis] Asset Acquisition [Axis] Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items] Prepaid expenses and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Accumulated Other Comprehensive Loss AOCI Attributable to Parent [Member] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Company match to employee contributions Defined Contribution Plan, Cost PROPERTY AND EQUIPMENT Property, Plant and Equipment Disclosure [Text Block] Non-current portion Contract with Customer, Liability, Noncurrent Title of Individual [Axis] Title of Individual [Axis] Other adjustments Effective Income Tax Rate Reconciliation, Other Adjustments, Amount Decrease in net income Decrease in Net Income Decrease in Net Income Plan Name [Axis] Plan Name [Axis] Capitalized 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Expense Weighted- average exercise price (in dollars per share) Share-Based Payment Arrangement, Option, Exercise Price Range, Outstanding, Weighted Average Exercise Price Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Trade name Acquired trade names and other intangible assets Trade Names [Member] Number of trade receivables in information services portfolio Number of Trade Receivables in Information Services Portfolio Number of Trade Receivables in Information Services Portfolio Retirement Plan Sponsor Location [Domain] Retirement Plan Sponsor Location [Domain] Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List] Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] State Current State and Local Tax Expense (Benefit) Total current assets Assets, Current Deferred: Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract] Financing cash flows used in finance leases Finance Lease, Principal Payments Consideration payable Business Combination, Contingent Consideration, Liability Restricted cash Restricted Cash Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Supplemental cash flow disclosures: Supplemental Cash Flow Information [Abstract] Percentage of total revenue Percentage of Total Revenue Percentage of Total Revenue Amortization of intangible assets Amortization Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Other income, net Other (income), net Other Nonoperating Income (Expense) Entity Filer Category Entity Filer Category Beginning balance Ending balance Financing Receivable, Allowance for Credit Loss Statement [Table] Statement [Table] Current Fiscal Year End Date Current Fiscal Year End Date Net Income Per Share Earnings Per Share, Policy [Policy Text Block] Lease and other long-term liabilities Lease and Other Liabilities, Noncurrent Lease and Other Liabilities, Noncurrent Recenue recognized as contract asset Contract with Customer, Asset, Reclassified to Receivable Schedule of Effective Income Tax Rate Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Unrecognized tax benefits beginning balance Unrecognized tax benefits ending balance Unrecognized Tax Benefits Income Tax Authority [Axis] Income Tax Authority [Axis] Debt Issuance Costs Debt, Policy [Policy Text Block] Current: Current Income Tax Expense (Benefit), Continuing Operations [Abstract] Schedule of Accumulated Other Comprehensive Loss Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Preferred stock, shares authorized (in shares) Preferred stock authorized for issuance (in shares) Preferred Stock, Shares Authorized Commissions capitalized in the current period Commissions Capitalized in the Current Period Commissions Capitalized in the Current Period Registered Retirement Savings Plan Supplemental Employee Retirement Plan [Member] Weighted-average grant date fair value (in USD per share) Granted (in USD 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 Amortization expense for 2028 Finite-Lived Intangible Asset, Expected Amortization, Year Five Buildings Building [Member] Schedule of Goodwill Schedule of Goodwill [Table Text Block] Goodwill measuring period adjustment Goodwill Measuring Period Adjustment Goodwill Measuring Period Adjustment Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Research and development credits Deferred Tax Assets, Tax Credit Carryforwards 2027 Finance Lease, Liability, to be Paid, Year Four Stock compensation Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-Based Compensation Cost Office Building - Richmond, Virginia Office Building - Richmond, Virginia [Member] Office Building - Richmond, Virginia Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Aggregate intrinsic value of options exercisable at end of period Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Intrinsic Value Business combinations cash escrow payment employee compensation post combination Business Combinations Cash Escrow Payment Employee Compensation Post Combination Business Combinations Cash Escrow Payment Employee Compensation Post Combination Financing Receivable, Allowance for Credit Loss [Line Items] Financing Receivable, Allowance for Credit Loss [Line Items] Total contract assets Contract with Customer, Asset, before Allowance for Credit Loss 2020 Credit Agreement 2020 Credit Agreement [Member] 2020 Credit Agreement CoStar Group, Inc. 2007 Stock Incentive Plan CoStar Group, Inc. 2007 Stock Incentive Plan [Member] Employee stock incentive plan name. Change in Contract with Customer, Liability [Roll Forward] Change in Contract with Customer, Liability [Roll Forward] Change in Contract with Customer, Liability [Roll Forward] 2024 Long-Term Debt, Maturity, Interest Payments, Year One Long-Term Debt, Maturity, Interest Payments, Year One ORGANIZATION Nature of Operations [Text Block] Depreciation and amortization Depreciation, Depletion and Amortization Deferred tax assets: Deferred Tax Assets, Gross [Abstract] Furniture, office equipment and vehicles Furniture and Fixtures [Member] Stated interest rate Debt Instrument, Interest Rate, Stated Percentage Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Deferred income taxes, net Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets $37.03 - $53.24 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. Business Combination and Asset Acquisition [Abstract] Total stockholders’ equity Beginning balance Ending balance Equity, Attributable to Parent Consolidation Items [Axis] Consolidation Items [Axis] Unrecognized tax benefits Unrecognized Tax Benefits that Would Impact Effective Tax Rate Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] Revenue Business Acquisition, Pro Forma Revenue Goodwill, impairment Goodwill, Impairment Loss Nondeductible compensation Effective Income Tax Rate Reconciliation, Nondeductible Expense, Compensation, Amount Effective Income Tax Rate Reconciliation, Nondeductible Expense, Compensation, Amount Restricted Stock Restricted Stock [Member] Valuation allowance Deferred Tax Assets, Valuation Allowance Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Finance lease obligations Finance Lease, Liability, to be Paid, Fiscal Year Maturity [Abstract] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Foreign currency translation adjustment Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Financing Receivable Portfolio Segment [Axis] Financing Receivable Portfolio Segment [Axis] Expected life (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Term Commitment fees and other Line of Credit Facility, Commitment Fee Amount Subsequent Events [Abstract] Subsequent Events [Abstract] Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest BureauxLocaux BureauxLocaux [Member] BureauxLocaux New deferrals recognized in connection with business acquisitions made Deferred income taxes, net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Other Marketplaces Other Marketplaces [Member] Other Marketplaces Commissions incurred Commissions Incurred Commissions Incurred Finite-Lived Intangible Assets Acquired as Part of Business Combination [Table] Finite-Lived Intangible Assets Acquired as Part of Business Combination [Table] Furniture and office equipment Furniture And Office Equipment [Member] Furniture And Office Equipment Numerator: Earnings Per Share Reconciliation [Abstract] Property, Plant and Equipment, Type [Axis] Long-Lived Tangible Asset [Axis] 2025 Long-Term Debt, Maturity, Interest Payments, Year Two Long-Term Debt, Maturity, Interest Payments, Year Two Fair Value, Inputs, Level 2 Fair Value, Inputs, Level 2 [Member] Emerging Growth Entity Emerging Growth Company Finance lease costs: Finance Lease Cost [Abstract] Finance Lease Cost Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Debt issuance costs, net Debt Issuance Costs, Net Intangible assets, net Intangible Assets, Net (Excluding Goodwill) Total deferred tax assets, prior to valuation allowance Deferred Tax Assets, Gross Fair value of identifiable net assets acquired Fair value of identifiable net assets acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Document Fiscal Period Focus Document Fiscal Period Focus Board of Directors Board of Directors [Member] Board of Directors 2024 Lessee, Operating Lease, Liability, to be Paid, Year One Useful life Estimated Useful Life Finite-Lived Intangible Asset, Useful Life Antidilutive Securities Excluded from Computation of Earnings Per Share, by Antidilutive Securities [Axis] Antidilutive Securities [Axis] 2027 Lessee, Operating Lease, Liability, to be Paid, Year Four 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 Stock-based compensation expense Share-Based Payment Arrangement, Noncash Expense 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 Total commissions expense Sales Commissions and Fees Common Stock Common Stock [Member] 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. Foreign Country Foreign Tax Authority [Member] Income taxes payable Accrued Income Taxes, Noncurrent Granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Net of Forfeitures City Area Code City Area Code Entity Address, Postal Zip Code Entity Address, Postal Zip Code Total deferred Deferred Other Tax Expense (Benefit) Product and Service [Axis] Product and Service [Axis] NET INCOME PER SHARE Earnings Per Share [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 Income Statement Location [Domain] Income Statement Location [Domain] Document Fiscal Year Focus Document Fiscal Year Focus Weighted-Average Grant Date Fair Value per Share Number of Matching RSU Shares Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] Lease liabilities Business Combination, Recognized Identifiable Asset Acquired and Liability Assumed, Lease Obligation Geographical [Domain] Geographical [Domain] Income tax penalties and interest expense (reversal) Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense Minimum Minimum [Member] Accrued reserve and other Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Reserves Property and equipment, net Property and equipment, net Property, Plant and Equipment, Net Range of exercise price, minimum, (in dollars per share) Share-Based Payment Arrangement, Option, Exercise Price Range, Lower Range Limit 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] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Total other comprehensive income (loss) Other comprehensive (loss) income Other Comprehensive Income (Loss), Net of Tax Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] CoStar Group, Inc. 2016 Stock Incentive Plan CoStar Group, Inc. 2016 Stock Incentive Plan [Member] CoStar Group, Inc. 2016 Stock Incentive Plan [Member] ASSETS Assets [Abstract] Purchase price Asset Acquisition, Price of Acquisition, Expected Interest capitalized for construction in process Interest Costs Capitalized Repurchase of restricted stock to satisfy tax withholding obligations Payment, Tax Withholding, Share-Based Payment Arrangement Write-offs charged against the allowance, net of recoveries and other Financing Receivable, Allowance for Credit Loss, Writeoff, after Recovery Net cash (used in) provided by financing activities Net Cash Provided by (Used in) Financing Activities Deferred income taxes, net Deferred Income Tax Assets, Net 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Income Taxes Receivable, Noncurrent Aggregate intrinsic value of options exercised Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period, Intrinsic Value 2022 Acquisitions 2022 Acquisitions [Member] 2022 Acquisitions Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Entity Address, City or Town Entity Address, City or Town Business Immo Business Immo [Member] Business Immo Summarized EBITDA Information by Operating Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] CoStar CoStar Suite [Member] CoStar Suite [Member] Schedule of Interest Expense Schedule of Interest Expense [Table Text Block] Schedule of Interest Expense Income taxes paid Income Taxes Paid Aircrafts Aircrafts [Member] Aircrafts Basis of Presentation Consolidation, Policy [Policy Text Block] Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] 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] Document Transition Report Document Transition Report Amortization of deferred commissions costs Amortization of deferred commissions costs Amortization of Deferred Sales Commissions Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Technology Technology-Based Intangible Assets [Member] Transaction costs Business Acquisition, Transaction Costs Foreign currency translation loss Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax Common stock, shares authorized (in shares) Common stock authorized for issuance (in shares) Common Stock, Shares Authorized Depreciation and other amortization Other Depreciation and Amortization Lease liabilities Operating and Finance Lease, Liability, Current Operating and Finance Lease, Liability, Current OnTheMarket plc OnTheMarket plc [Member] OnTheMarket plc Public Float Entity Public Float Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Property, Plant and Equipment [Abstract] Property, Plant and Equipment [Abstract] Increase (decrease) in valuation allowance Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount 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] Title of Individual [Domain] Title of Individual [Domain] Conversion ratio Stockholders' Equity Note, Stock Split, Conversion Ratio Summarized Information by Operating Segment, Assets and Liabilities Reconciliation of Assets from Segment to Consolidated [Table Text Block] Credit loss expense Accounts Receivable, Credit Loss Expense (Reversal) Additional paid-in capital Additional Paid in Capital 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 Canceled (in USD per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value 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 Number of trade receivables in other marketplaces portfolio segment Number of Trade Receivables in Other Marketplaces Portfolio Segment Number of Trade Receivables in Other Marketplaces Portfolio Segment Deferred income taxes, net Deferred Income Tax Expense (Benefit) Subsequent Event Type [Axis] Subsequent Event Type [Axis] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Liabilities incurred Business Combination, Consideration Transferred, Liabilities Incurred Number of trade receivables in multifamily portfolio Number of Trade Receivables in Multifamily Portfolio Number of Trade Receivables in Multifamily Portfolio Present value of lease liabilities Finance Lease, Liability Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table] Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table] Accrued wages and commissions Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Current Liabilities, Accrued Wages And Commissions Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Current Liabilities, Accrued Wages And Commissions Income Taxes Income Tax, Policy [Policy Text Block] Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Document Financial Statement Error Correction Document Financial Statement Error Correction [Flag] Amortization expense for 2026 Finite-Lived Intangible Asset, Expected Amortization, Year Three Canceled (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period 2024 Long-Term Debt, Maturity, Year One Aggregate intrinsic value of options outstanding at end of period Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Intrinsic Value Purchase price before adjustments Business Combination, Acquisition Price Before Working Capital and Other Adjustments Business Combination, Acquisition Price Before Working Capital and Other Adjustments Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Public Offering Public Offering [Member] Public Offering Entity Registrant Name Entity Registrant Name Stock options, restricted stock awards and restricted stock units (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements Lease liabilities Deferred Tax Assets, Lease Liabilities Deferred Tax Assets, Lease Liabilities Term of credit facility Line of Credit Facility, Expiration Period Computer hardware and software Computer Hardware And Software [Member] Computer Hardware And Software Amortization expense for 2025 Finite-Lived Intangible Asset, Expected Amortization, Year Two Range of exercise price, maximum, (in dollars per share) Share-Based Payment Arrangement, Option, Exercise Price Range, Upper Range Limit Deferred stock unit, granted percentage Deferred Stock Unit, Granted Percentage Deferred Stock Unit, Granted Percentage Cost of revenues Cost of Sales [Member] Documents Incorporated by Reference Documents Incorporated by Reference [Text Block] Accumulated Other Comprehensive Income (Loss) Net of Tax [Abstract] Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Auditor Name Auditor Name Document Period End Date Document Period End Date Deferred revenue Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Deferred Revenue 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”) Accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Multifamily Multifamily Online Marketplace [Member] Multifamily Online Marketplace [Member] Credit Loss [Abstract] Exercisable at end of period (in dollars per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Weighted Average Exercise Price Payments of long-term debt assumed in acquisition Repayments of Long-Term Debt Weighted-average discount rate Finance Lease, Weighted Average Discount Rate, Percent Long-term lease liabilities Finance Lease, Liability, Noncurrent Business Acquisition, Pro Forma Information Business Acquisition, Pro Forma Information [Table Text Block] Entity Central Index Key Entity Central Index Key Amortization of Senior Notes discount and issuance costs Amortization of Debt Issuance Costs and Discounts Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Total stock-based compensation expense Compensation expense Share-Based Payment Arrangement, Expense Effect of 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Business Acquisition, Pro Forma Earnings Per Share, Basic Performance Based RSAs Without Market Condition Performance Based RSAs Without Market Condition [Member] Performance Based RSAs Without Market Condition [Member] ROU Assets Finance Lease, Right-of-Use Asset, after Accumulated Amortization Accrued wages and commissions Employee-related Liabilities, Current INVESTMENTS AND FAIR VALUE MEASUREMENTS Fair Value Disclosures [Text Block] Number of business segments Number of operating segments Number of Operating Segments Cash and Cash Equivalents [Abstract] Cash and Cash Equivalents [Abstract] Current-period provision (release) for expected credit losses Financing Receivable, Credit Loss, Expense (Reversal) Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Stock issued for equity offerings, net of transaction costs Stock Issued During Period, Value, New Issues 2027 Long-Term Debt, Maturity, Interest Payments, Year Four Long-Term Debt, Maturity, Interest Payments, Year Four Weighted-average remaining lease term in years Operating Lease, Weighted Average Remaining Lease Term Software development Research and Development Expense, Software (Excluding Acquired in Process Cost) Revenues Revenue from Contract with Customer, Excluding Assessed Tax Amendment Flag Amendment Flag INTANGIBLE ASSETS Intangible Assets Disclosure [Text Block] Deferred sales commissions of impaired Deferred Sales Commissions, Impairment Deferred Sales Commissions, Impairment Reclassification out of accumulated other comprehensive loss Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax Income tax credit carryforward Tax Credit Carryforward, Amount Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Cash paid for acquisitions, net of cash acquired Cash paid for acquisitions, net Payments to Acquire Businesses, Net of Cash Acquired Management stock purchase plan (in shares) Share-Based Payment Arrangement, Shares Withheld for Tax Withholding Obligation Weighted-average discount rate Operating Lease, Weighted Average Discount Rate, Percent Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activities 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 Credit Facility [Domain] Credit Facility [Domain] Business Combinations Business Combinations Policy [Policy Text Block] Basis spread Debt Instrument, Basis Spread on Variable Rate Useful life Property, Plant and Equipment, Useful Life GOODWILL Goodwill Disclosure [Text Block] Long-term debt, net Long-term debt, net Long-Term Debt, Excluding Current Maturities Leasehold improvements Leasehold Improvements [Member] Weighted-average remaining lease term in years Finance Lease, Weighted Average Remaining Lease Term Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Net deferred tax liabilities Deferred Tax Liabilities, Net Selling and marketing (excluding customer base amortization) Selling and marketing (excluding customer base amortization) Selling and Marketing Expense [Member] 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 Software development Software development Software Development [Member] 2.800% Senior Notes 2.800 Senior Notes [Member] 2.800 Senior Notes Retirement Plan Sponsor Location [Axis] Retirement Plan Sponsor Location [Axis] Intangible assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill Summary 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Finance leases Right-of-Use Asset Obtained in Exchange for Finance Lease Liability Intangible Assets, Net (Excluding Goodwill) [Abstract] Intangible Assets, Net (Excluding Goodwill) [Abstract] Interest income (expense), net Interest (income) expense, net Interest Income (Expense), Nonoperating, Net Operating expenses: Operating Expenses [Abstract] Less: imputed interest Finance Lease, Liability, Undiscounted Excess Amount REVENUE FROM CONTRACTS WITH CUSTOMERS Revenue from Contract with Customer [Text Block] Decrease for settlements with taxing authorities Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities Purchase and construction of Richmond assets Payments for land and building Payments to Acquire Property, Plant, and Equipment Additional Paid-in Capital Additional Paid-in Capital [Member] Document Annual Report Document Annual Report Weighted-average remaining contractual life (in years) Share-Based Payment Arrangement, Option, Exercise Price Range, Outstanding, Weighted Average Remaining Contractual Term Allowance for credit losses Deferred Tax Asset, Tax Deferred Expense, Reserve and Accrual, Accounts Receivable, Allowance for Credit Loss Vehicles Vehicles [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Total assets Total assets Assets Amortization of acquired intangible assets in operating expenses Amortization Of Intangible Assets, Net Of Adjustments Amortization Of Intangible Assets, Net Of Adjustments Thereafter Finance Lease, Liability, to be Paid, after Year Five Cover [Abstract] Cover [Abstract] SUBSEQUENT EVENTS Subsequent Events [Text Block] Stock-based compensation expense APIC, Share-Based Payment Arrangement, Increase for Cost Recognition 2028 Long-Term Debt, Maturity, Year Five Amortization of Senior Notes discount and issuance costs Amortization of Debt Issuance Costs Effects of foreign currency Contract with Customer, Asset, Effects of Currency Translation Contract with Customer, Asset, Effects of Currency Translation Operating cash flows used in finance leases Finance Lease, Interest Payment on Liability Vested (in USD 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 Canceled or expired (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures and Expirations in Period Operating lease liabilities Lessee, Operating Lease, Liability, to be Paid Remaining performance obligation Revenue, Remaining Performance Obligation, Amount Pension Plan Pension Plan [Member] Subsidiary, Sale of Stock [Line Items] Subsidiary, Sale of Stock [Line Items] Total operating expenses Operating Expenses Amortization of ROU assets Finance Lease, Right-of-Use Asset, Amortization SEGMENT REPORTING Segment Reporting Disclosure [Text Block] Net increase in cash and cash equivalents Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Equity Component [Domain] Equity Component [Domain] Less: current portion of lease liabilities Finance Lease, Liability, Current State and Local Jurisdiction State and Local Jurisdiction [Member] Net operating losses Deferred Tax Assets, Operating Loss Carryforwards Debt Instrument [Line Items] Debt Instrument [Line Items] 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 Information services Information Services [Member] Information services [Member] Entity Current Reporting Status Entity Current Reporting Status Income from operations Operating Income (Loss) 2026 Long-Term Debt, Maturity, Interest Payments, Year Three Long-Term Debt, Maturity, Interest Payments, Year Three Property and equipment, net Deferred Tax Liabilities, Property, Plant and Equipment Deferred commissions Increase (Decrease) Deferred Commissions Increase (Decrease) Deferred Commissions Restricted stock grants surrendered (in shares) Stock Issued During Period, Shares, Restricted Stock Award, Forfeited Total deferred tax liabilities Deferred Tax Liabilities, Gross Statement [Line Items] Statement [Line Items] Property and Equipment, Net Property, Plant and Equipment, Policy [Policy Text Block] Other comprehensive income (loss), net of tax Other Comprehensive Income (Loss), Net of Tax [Abstract] Audit Information [Abstract] Audit Information 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] Customer base Customer Relationships [Member] Line of credit facility, amount outstanding Long-Term Line of Credit Stockholders’ equity: Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]