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(in shares) Share-Based Compensation Arrangement By Share-Based Payment Award, Options, Assumed In Acquisition Share-Based Compensation Arrangement By Share-Based Payment Award, Options, Assumed In Acquisition Counterparty Name [Domain] Counterparty Name [Domain] 2027 Lessee, Operating Lease, Liability, to be Paid, Year Two Number of business segments Number of operating segments Number of Operating Segments Conversion ratio Stockholders' Equity Note, Stock Split, Conversion Ratio Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Weighted average remaining contract life, outstanding (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Thereafter Lessee, Operating Lease, Liability, to be Paid, Due After Year Four Lessee, Operating Lease, Liability, to be Paid, Due After Year Four Purchases of equity securities Payments to Acquire Equity Securities, 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Transition Report Rentable square feet Net Rentable Area Total Finance Lease, Liability, to be Paid Underlying Securities Award Underlying Securities Amount Building occupied (as a percent) Asset Acquisition, Owner Occupancy Percentage Asset Acquisition, Owner Occupancy Percentage Equity Component [Domain] Equity Component [Domain] Document Period End Date Document Period End Date PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Canceled or expired (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures and Expirations in Period INCOME TAXES Income Tax Disclosure [Text Block] CoStar Group, Inc. 2016 Stock Incentive Plan CoStar Group, Inc. 2016 Stock Incentive Plan [Member] CoStar Group, Inc. 2016 Stock Incentive Plan [Member] Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Thereafter 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Total property and equipment, net Property, Plant and Equipment, Net Unrealized gains on investments and deal-contingent foreign currency forward contracts Unrealized Gain (Loss) On Investments And Derivatives Unrealized Gain (Loss) On Investments And Derivatives Preferred stock authorized for issuance (in shares) Preferred Stock, Shares Authorized Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Stock repurchase Payments for Repurchase of Common Stock Adoption Date Trading Arrangement Adoption Date Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Multifamily Multifamily Online Marketplace [Member] Multifamily Online Marketplace [Member] Accounts receivable Increase (Decrease) in Accounts Receivable Inventories Inventory, Policy [Policy Text Block] Current portion Deferred Income, Current Entity Current Reporting Status Entity Current Reporting Status Term of contract Lessee, Operating Lease, Term of 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Contract with Customer, Liability Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Long-term lease liabilities Finance Lease, Liability, Noncurrent Equity investment Short-term investments: Equity Securities, FV-NI, Current Common stock issued for Matterport Acquisition Stock Issued During Period, Value, Acquisitions Fair value of identifiable net assets acquired Business Combination, Recognized Asset Acquired to Liability Assumed, Excess (Less) Anti-dilutive securities (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount All Adjustments to Compensation All Adjustments to Compensation [Member] Amendment Flag Amendment Flag 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 2027 Long-Term Debt, Maturity, Year Two Accrued interest Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss Schedule of Acquired Finite-Lived Intangible Assets by Major Class Schedule of Acquired Finite-Lived Intangible Assets by Major Class [Table Text Block] Software development Software development Software Development [Member] LEASES Lessee, Operating Leases [Text Block] Termination Date Trading Arrangement Termination Date Net cash used in financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Measure: Measure [Axis] 2.800% Senior Notes due July 15, 2030 2.800 Senior Notes [Member] 2.800 Senior Notes Beginning balance Ending balance Financing Receivable, Allowance for Credit Loss, Excluding Accrued Interest Foreign currency transaction gain (loss) Realized Gain (Loss), Foreign Currency Transaction, before Tax Total contract assets 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Combination, Pro Forma Information, Pro Forma Earnings Per Share, Basic Lease income Operating Lease, Lease Income SUBSEQUENT EVENTS Subsequent Events [Text Block] Insider Trading Arrangements [Line Items] Security Exchange Name Security Exchange Name Information Services Information Services [Member] Information services [Member] Remainder of 2025 Long-Term Debt, Maturity, Remainder of Fiscal Year Other Revenues Product and Service, Other [Member] Total liabilities Total liabilities Liabilities 2028 Long-Term Debt, Maturity, Interest Payments, Year Three Long-Term Debt, Maturity, Interest Payments, Year Three Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Product Concentration Risk Product Concentration Risk [Member] Maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Deferred commissions Increase (Decrease) Deferred Commissions Increase (Decrease) Deferred Commissions Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Operating expenses: Operating Expenses [Abstract] Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Other current liabilities Other Liabilities, Current Statement [Line Items] Statement [Line Items] Consolidation Items [Axis] Consolidation Items [Axis] Variable Rate [Axis] Variable Rate [Axis] Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Cash and cash equivalents Cash and Cash Equivalent Counterparty Name [Axis] Counterparty Name [Axis] Schedule of Unvested Restricted Stock Awards Activity Share-Based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block] Common Stock Common Stock [Member] Vested (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period Acquired customer base Customer Contracts [Member] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Non-NEOs Non-NEOs [Member] Finance lease obligations Finance Lease, Liability, to be Paid, Fiscal Year Maturity [Abstract] Subsidiary, Sale of Stock [Line Items] Subsidiary, Sale of Stock [Line Items] Net decrease in cash, cash equivalents, and restricted cash Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation