CoStar (CSGP) 10-Q 27 Oct 16 2016 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2016	Oct. 21, 2016
Document and Entity Information [Abstract]
Entity Registrant Name	COSTAR GROUP INC
Entity Central Index Key	1,057,352
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		32,593,441

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Revenues	$ 212,711	$ 189,078	$ 619,319	$ 518,755
Cost of revenues	42,222	53,728	127,801	143,758
Gross margin	170,489	135,350	491,518	374,997
Operating expenses:
Selling and marketing	75,414	80,506	231,086	242,418
Software development	19,357	17,048	56,539	49,040
General and administrative	30,572	31,074	88,275	86,346
Purchase amortization	5,550	7,153	17,602	21,260
Total operating expenses	130,893	135,781	393,502	399,064
Income (loss) from operations	39,596	(431)	98,016	(24,067)
Interest and other income	344	42	587	473
Interest and other expense	(2,498)	(2,363)	(7,462)	(7,060)
Income (loss) before income taxes	37,442	(2,752)	91,141	(30,654)
Income tax expense (benefit), net	14,241	2,610	35,643	(4,199)
Net income (loss)	$ 23,201	$ (5,362)	$ 55,498	$ (26,455)
Net income (loss) per share-basic (in dollars per share)	$ 0.72	$ (0.17)	$ 1.73	$ (0.83)
Net income (loss) per share-diluted (in dollars per share)	$ 0.72	$ (0.17)	$ 1.71	$ (0.83)
Weighted average outstanding shares-basic (in shares)	32,186	31,980	32,152	31,934
Weighted average outstanding shares-diluted (in shares)	32,440	31,980	32,423	31,934

CONDENSED CONSOLIDATED STATEME3

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 23,201	$ (5,362)	$ 55,498	$ (26,455)
Other comprehensive loss, net of tax
Foreign currency translation adjustment	(596)	(965)	(3,054)	(719)
Net decrease in unrealized loss on investments	46	8	275	256
Total other comprehensive loss	(550)	(957)	(2,779)	(463)
Total comprehensive income (loss)	$ 22,651	$ (6,319)	$ 52,719	$ (26,918)

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 522,099	$ 421,818
Short-term investments	1,171	0
Accounts receivable, net of allowance for doubtful accounts of approximately $7,324 and $7,478 as of September 30, 2016 and December 31, 2015, respectively	47,461	40,276
Income tax receivable	1,049	430
Prepaid expenses and other current assets	11,663	10,209
Total current assets	583,443	472,733
Long-term investments	9,911	15,507
Deferred income taxes, net	8,153	9,107
Property and equipment, net	85,366	88,311
Goodwill	1,256,353	1,252,945
Intangible assets, net	207,113	238,318
Deposits and other assets	2,248	2,650
Total assets	2,152,587	2,079,571
Current liabilities:
Current portion of long-term debt	21,825	16,746
Accounts payable	9,861	9,673
Accrued wages and commissions	32,443	31,045
Accrued expenses	33,252	31,423
Deferred gain on the sale of building	2,523	2,523
Income taxes payable	9,079	46
Deferred rent	2,612	1,687
Deferred revenue	41,864	42,138
Total current liabilities	153,459	135,281
Long-term debt, less current portion	315,694	338,366
Deferred gain on the sale of building	19,346	21,239
Deferred rent	29,193	29,628
Deferred income taxes, net	9,185	4,585
Income taxes payable	7,012	6,692
Total liabilities	533,889	535,791
Stockholders' equity:
Total stockholders’ equity	1,618,698	1,543,780
Total liabilities and stockholders’ equity	$ 2,152,587	$ 2,079,571

CONDENSED CONSOLIDATED BALANCE5

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Current assets:
Allowance for doubtful accounts	$ 7,324	$ 7,478

CONDENSED CONSOLIDATED STATEME6

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Operating activities:
Net income (loss)	$ 55,498	$ (26,455)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation	17,927	14,445
Amortization	35,114	44,562
Amortization of debt issuance costs	2,407	2,486
Impairment loss	0	2,778
Excess tax benefit from stock-based compensation	(4,728)	(7,970)
Stock-based compensation expense	26,981	25,169
Deferred income tax expense (benefit), net	5,554	(13,702)
Provision for losses on accounts receivable	6,462	5,490
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable	(13,808)	(13,279)
Prepaid expenses and other current assets	(1,398)	263
Deposits and other assets	473	411
Accounts payable and other liabilities	12,864	30,085
Deferred revenue	386	5,433
Net cash provided by operating activities	143,732	69,716
Investing activities:
Proceeds from sale and settlement of investments	4,700	1,900
Purchases of property and equipment and other assets	(11,692)	(27,953)
Acquisitions, net of cash acquired	(10,443)	(177,476)
Net cash used in investing activities	(17,435)	(203,529)
Financing activities:
Payments of long-term debt	(20,000)	(15,000)
Excess tax benefit from stock-based compensation	4,728	7,970
Repurchase of restricted stock to satisfy tax withholding obligations	(14,573)	(15,816)
Proceeds from exercise of stock options and employee stock purchase plan	4,791	5,350
Net cash used in financing activities	(25,054)	(17,496)
Effect of foreign currency exchange rates on cash and cash equivalents	(962)	(194)
Net increase (decrease) in cash and cash equivalents	100,281	(151,503)
Cash and cash equivalents at the beginning of period	421,818	527,012
Cash and cash equivalents at the end of period	$ 522,099	$ 375,509

ORGANIZATION

ORGANIZATION	9 Months Ended
	Sep. 30, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
ORGANIZATION	ORGANIZATION CoStar Group, Inc. (the “Company” or “CoStar”) provides information, analytics and online marketplace services to the commercial real estate and related business community through its comprehensive, proprietary database of commercial real estate information covering the United States (“U.S.”), the United Kingdom (“U.K.”), and parts of Canada, Spain, Germany and France. The Company provides online marketplaces for commercial real estate, apartment rentals, lands for sale and businesses for sale. The Company operates within two operating segments, North America and International, and its services are typically distributed to its clients under subscription-based license agreements that renew automatically, a majority of which have a term of one year .

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended
	Sep. 30, 2016
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation The condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Accounting policies are consistent for each operating segment. Interim Financial Statements The accompanying unaudited condensed consolidated financial statements of the Company have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information. In the opinion of the Company’s management, the financial statements reflect all adjustments necessary to present fairly the Company’s financial position at September 30, 2016 and December 31, 2015 , the results of its operations for the three and nine months ended September 30, 2016 and 2015 , its comprehensive income (loss) for the three and nine months ended September 30, 2016 and 2015 , and its cash flows for the nine months ended September 30, 2016 and 2015 . These adjustments are of a normal recurring nature. Certain notes and other information have been condensed or omitted from the interim financial statements presented in this Quarterly Report on Form 10-Q. Therefore, these financial statements should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2015 . The results of operations for the three and nine months ended September 30, 2016 are not necessarily indicative of future financial results. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company evaluates its estimates and assumptions, including those related to revenue recognition, allowance for doubtful accounts, useful lives of property and equipment and intangible assets, recoverability of long-lived assets and intangible assets with definite lives, goodwill, income taxes, fair value of equity instruments, fair value of auction rate securities, accounting for business combinations and contingencies, among others. The Company bases these estimates on historical and anticipated results, trends, and various other assumptions that it believes are reasonable, including assumptions as to future events. These estimates form the basis for making judgments about the carrying values of assets and liabilities and recorded revenue and expenses. Actual results could differ from these estimates. Reclassifications Certain previously reported amounts in the condensed consolidated balance sheets as of December 31, 2015 have been reclassified to conform to the Company's current presentation to reflect current income taxes payable separately, which was previously included in accrued expenses. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED) Advertising Costs The Company expenses advertising costs as incurred. Advertising costs include e-commerce, television, radio, print and other media advertising. Advertising costs were approximately $27 million and $34 million for the three months ended September 30, 2016 and 2015 , respectively. Advertising costs were approximately $95 million and $113 million for the nine months ended September 30, 2016 and 2015 , respectively. Foreign Currency Translation The Company’s functional currency in its foreign locations is the local currency. Assets and liabilities are translated into U.S. dollars using the exchange rates as of the balance sheet dates. Revenues, expenses, gains and losses are translated at the average exchange rates in effect during each period. Gains and losses resulting from translation are included in accumulated other comprehensive loss. Net gains or losses resulting from foreign currency exchange transactions are included in the condensed consolidated statements of operations. There were no material gains or losses from foreign currency exchange transactions for the three and nine months ended September 30, 2016 and 2015 . Accumulated Other Comprehensive Loss The components of accumulated other comprehensive loss were as follows (in thousands): September 30, December 31, Foreign currency translation adjustment $ (10,213 ) $ (7,159 ) Accumulated net unrealized loss on investments, net of tax (160 ) (435 ) Total accumulated other comprehensive loss $ (10,373 ) $ (7,594 ) There were no amounts reclassified out of accumulated other comprehensive loss to the condensed consolidated statements of operations for the three and nine months ended September 30, 2016 and 2015 . Net Income (Loss) Per Share Net income (loss) per share is computed by dividing net income (loss) by the weighted average number of common shares outstanding during the period on a basic and diluted basis. The Company’s potentially dilutive securities include stock options and restricted stock. Diluted net income (loss) per share considers the impact of potentially dilutive securities except in periods in which there is a net loss, as the inclusion of the potentially dilutive common shares would have an anti-dilutive effect. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED) Net Income (Loss) Per Share — (Continued) The following table sets forth the calculation of basic and diluted net income (loss) per share (in thousands, except per share data): Three Months Ended Nine Months Ended Numerator: 2016 2015 2016 2015 Net income (loss) $ 23,201 $ (5,362 ) $ 55,498 $ (26,455 ) Denominator: Denominator for basic net income (loss) per share — weighted-average outstanding shares 32,186 31,980 32,152 31,934 Effect of dilutive securities: Stock options and restricted stock 254 — 271 — Denominator for diluted net income (loss) per share — weighted-average outstanding shares 32,440 31,980 32,423 31,934 Net income (loss) per share — basic $ 0.72 $ (0.17 ) $ 1.73 $ (0.83 ) Net income (loss) per share — diluted $ 0.72 $ (0.17 ) $ 1.71 $ (0.83 ) Stock options to purchase approximately 89,000 and 184,000 shares that were outstanding for the three and nine months ended September 30, 2016 , respectively, were not included in the computation of diluted net income per share because the inclusion would have an anti-dilutive effect. The Company did not consider the impact of potentially dilutive securities for the three and nine months ended September 30, 2015 when calculating the diluted net loss per share because the inclusion of the potentially dilutive common shares would have an anti-dilutive effect. Shares underlying restricted common stock awards that vest based on Company performance and service conditions, that have not been achieved as of the end of the period are not included in the computation of basic or diluted earnings per share. Shares underlying restricted stock units that vest based on Company service conditions, that have not been achieved as of the end of the period are not included in the computation of basic or diluted earnings per share. The following table summarizes the shares underlying the performance-based restricted stock awards and service-based restricted stock units excluded from the basic and diluted calculation (in thousands): Three Months Ended Nine Months Ended 2016 2015 2016 2015 Performance-based restricted stock awards 72 55 72 55 Service-based restricted stock units 1 1 1 1 Total shares excluded from computation 73 56 73 56 Stock-Based Compensation Equity instruments issued in exchange for employee services are accounted for using a fair-value based method and the fair value of such equity instruments is recognized as expense in the condensed consolidated statements of operations. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED) Stock-Based Compensation — (Continued) Stock-based compensation expense is measured at the grant date of the stock-based awards that vest over set time periods based on their fair values, and is recognized on a straight line basis as expense over the vesting periods of the awards, net of an estimated forfeiture rate. For equity instruments that vest based on performance, the Company assesses the probability of the achievement of the performance conditions at the end of each reporting period, or more frequently based upon the occurrence of events that may change the probability of whether the performance conditions would be met. If the Company's initial estimates of the achievement of the performance conditions change, the related stock-based compensation expense and timing of recognition may fluctuate from period to period based on those estimates. For equity instruments that vest based on a performance condition and a market condition, the Company estimates the fair value of each equity instrument granted on the date of grant using a Monte-Carlo simulation model. This pricing model uses multiple simulations to evaluate the probability of achieving the market condition to calculate the fair value of the awards. Stock-based compensation expense is updated based on the expected achievement of the related performance conditions at the end of each reporting period. If the performance conditions are not met, no stock-based compensation expense will be recognized, and any previously recognized stock-based compensation expense will be reversed. Cash flows resulting from excess tax benefits are classified as part of cash flows from operating and financing activities. Excess tax benefits represent tax benefits for stock-based compensation in excess of the associated deferred tax asset for such equity compensation recorded as an increase to stockholders' equity. Net cash proceeds from the exercise of stock options and the purchase of shares under the Employee Stock Purchase Plan (“ESPP”) were approximately $1 million and $646,000 for the three months ended September 30, 2016 and 2015 , respectively. Net cash proceeds from the exercise of stock options and the purchase of shares under the ESPP were approximately $5 million for each of the nine months ended September 30, 2016 and 2015 . The Company realized approximately $398,000 and $418,000 of excess tax benefits from stock options exercised and restricted stock awards vested during the three months ended September 30, 2016 and 2015 , respectively. The Company realized approximately $5 million and $8 million of excess tax benefits from stock options exercised and restricted stock awards vested during the nine months ended September 30, 2016 and 2015 , respectively. Stock-based compensation expense for stock options and restricted stock issued under equity incentive plans and stock purchases under the ESPP included in the Company’s results of operations were as follows (in thousands): Three Months Ended Nine Months Ended 2016 2015 2016 2015 Cost of revenues $ 1,396 $ 1,533 $ 4,209 $ 4,242 Selling and marketing 1,676 1,411 4,920 3,595 Software development 1,684 1,602 4,902 4,318 General and administrative 4,555 4,766 12,950 13,014 Total stock-based compensation $ 9,311 $ 9,312 $ 26,981 $ 25,169 Options to purchase 3,367 shares were exercised during the three months ended September 30, 2016 . There were no options exercised during the three months ended September 30, 2015 . Options to purchase 24,078 and 41,068 shares were exercised during the nine months ended September 30, 2016 and 2015 , respectively. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED) Debt Issuance Costs Costs incurred in connection with the issuance of long-term debt are capitalized and amortized as interest expense over the term of the related debt using the effective interest method. These amounts are reflected in the consolidated balance sheets as direct deductions from a combination of the current and long-term portions of debt. Upon a refinancing, previously capitalized debt issuance costs are expensed and included in loss on extinguishment of debt if the Company determines that there has been a substantial modification of the related debt. If the Company determines that there has not been a substantial modification of the related debt, any previously capitalized debt issuance costs are amortized as interest expense over the term of the new debt instrument using the effective interest method. The Company had capitalized debt issuance costs, net of amortization, of approximately $7 million and $10 million as of September 30, 2016 and December 31, 2015 , respectively. The debt issuance costs are associated with the financing commitment received from JPMorgan Chase Bank, N.A. (“J.P. Morgan Bank”) on April 27, 2011, the subsequent term loan facility and revolving credit facility established under a credit agreement dated February 16, 2012 (the “2012 Credit Agreement”), the financing commitment received from J.P. Morgan Bank, Bank of America, N.A., SunTrust Bank and Wells Fargo Bank, National Association on February 28, 2014, and the subsequent term loan facility and revolving credit facility established under a credit agreement dated April 1, 2014 (the “2014 Credit Agreement”). See Note 8 for additional information regarding the term loan facility and revolving credit facility. The Company amortized debt issuance costs of approximately $797,000 and $830,000 for the three months ended September 30, 2016 and 2015 , respectively. The Company amortized debt issuance costs of approximately $2 million for each of the nine months ended September 30, 2016 and 2015 . Business Combinations The Company allocates the purchase consideration to the tangible assets acquired, liabilities assumed and intangible assets acquired based on their estimated fair values. The excess of the fair value of purchase consideration over the fair values of these identifiable assets and liabilities is recorded as goodwill. Such valuations require management to make significant estimates and assumptions, especially with respect to intangible assets. Significant estimates in valuing certain intangible assets include, but are not limited to, future expected cash flows from acquired customer bases, acquired database technology, and acquired trade names from a market participant's perspective, useful lives and discount rates. During the measurement period, the Company may record adjustments to the assets acquired and liabilities assumed. Any adjustments to provisional amounts that are identified during the measurement period are recorded in the reporting period in which the adjustment amounts are determined. Upon the conclusion of the measurement period, any subsequent adjustments are recorded to earnings. See Note 3 for additional information regarding the Company's business combinations. Recent Accounting Pronouncements There have been no developments to the Recent Accounting Pronouncements discussion included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2015 , including the expected dates of adoption and estimated effects on the Company’s condensed consolidated financial statements, except for the following: 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED) Recent Accounting Pronouncements — (Continued) In May 2014, the Financial Accounting Standards Board (“FASB”) and International Accounting Standards Board (“IASB”) jointly issued a new revenue recognition standard that is designed to improve financial reporting by creating common recognition guidance for GAAP and International Financial Reporting Standards (“IFRS”). This guidance provides a robust framework for addressing revenue issues, improves the comparability of revenue recognition practices across industries, provides useful information to users of financial statements through improved disclosure requirements and simplifies the presentation of financial statements. The core principle of the guidance is that an entity should recognize revenue to depict the transfer of promised goo ds or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. From March to May of 2016, amendments to the new revenue recognition standard were issued to clarify numerous accounting topics, including, but not limited to (i) the implementation guidance on principal versus agent considerations, (ii) the identification of performance obligations, (iii) the licensing implementation guidance, (iv) the objective of the collectability criterion and (v) the application of the variable consideration guidance and modified retrospective transition method. This guidance permits the use of either a full retrospective method or a modified retrospective approach. The modified retrospective approach would be applied only to the most current period presented along with a cumulative-effect adjustment at the date of adoption. This guidance will be effective for annual reporting periods beginnin g after December 15, 2017, although companies may adopt the standard as early as annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. The Company has not yet determined when it will adopt the standard or selected a transition method and is currently evaluating the impact this guidance will have on its financial statements and related disclosures. In February 2016, the FASB issued authoritative lease guidance to increase transparency and comparability among organizations. The guidance requires a company to recognize lease assets and lease liabilities on the balance sheet as well as disclose key information about leasing arrangements. This guidance is effective on a modified retrospective basis for annual reporting periods beginning after December 15, 2018, including interim periods within that reporting period. Early application is permitted. The Company is currently evaluating the impact this guidance will have on its financial statements and related disclosures. In March 2016, the FASB issued authoritative guidance to simplify several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification of share-based payment transactions on the statement of cash flows. The guidance requires a company to (i) recognize all excess tax benefits and tax deficiencies as income tax expense or benefit in the statement of operations using a prospective transition method, (ii) recognize excess tax benefits in the current period regardless of whether the benefit reduces taxes payable using a modified retrospective transition method, and (iii) classify all excess tax benefits as operating activities within the statement of cash flows using either a prospective transition method or a retrospective transition method. The guidance also allows a company to (i) elect whether to estimate the number of awards expected to vest or account for forfeitures when they occur, and (ii) withhold up to the maximum statutory tax rate in the applicable jurisdiction for awards, both of which should be applied using a modified retrospective transition method. Finally, the guidance requires a company to classify the cash paid by an employer when directly withholding shares for tax withholding purposes as a financing activity within the statement of cash flows using a retrospective transition method. This guidance is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. Early application is permitted. The Company is currently evaluating the impact this guidance will have on its financial statements and related disclosures. In June 2016, the FASB issued authoritative guidance designed to provide financial statement users with more information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. When determining such expected credit losses, the guidance requires companies to apply a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. This guidance is effective on a modified retrospective basis for annual reporting periods beginning after December 15, 2019, including interim periods within that reporting period. C ompanies may adopt the standard as early as annual reporting periods beginning after December 15, 2018 . The Company is currently evaluating the impact this guidance will have on its financial statements and related disclosures. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED) Recent Accounting Pronouncements — (Continued) In August 2016, the FASB issued authoritative guidance designed to reduce the existing diversity in how certain cash receipts and cash payments are presented and classified in the consolidated statements of cash flows. This guidance is effective on a retrospective basis for annual reporting periods beginning after December 15, 2017, including interim periods within that reporting period. Early application is permitted. This guidance is not expected to have a material impact on the Company's consolidated statements of cash flows and related disclosures.

ACQUISITION

ACQUISITION	9 Months Ended
	Sep. 30, 2016
Business Combinations [Abstract]
ACQUISITION	ACQUISITION Pursuant to the definitive agreement and plan of merger with Network Communications, Inc. (“NCI”) dated April 27, 2015 (the “Merger Agreement”), on June 1, 2015, the Company acquired 100% of the outstanding stock of NCI and the related Apartment Finder business (collectively referred to as “Apartment Finder”) from the former stockholders of NCI. Apartment Finder provides lead generation, advertising and Internet marketing solutions to property managers and owners through its main service, ApartmentFinder.com TM . The acquisition furthered the Company's expansion into the multifamily vertical. In consideration for the purchase of Apartment Finder, on June 1, 2015, the Company paid $173 million in cash, including an estimated $3 million in connection with a preliminary adjustment for net working capital as of the closing date. Pursuant to the terms of the Merger Agreement, the purchase price was increased by approximately $21,000 following the final determination of the net working capital of NCI as of the closing date, and this amount was paid to NCI in the third quarter of 2015. The Company applied the acquisition method to account for the Apartment Finder transaction, which requires that, among other things, assets acquired and liabilities assumed be recorded at their fair values as of the acquisition date. The following table summarizes the amounts for acquired assets and liabilities recorded at their fair values as of the acquisition date (in thousands): Cash and cash equivalents $ 39 Accounts receivable 4,556 Goodwill 107,692 Acquired trade names and other intangible assets 23,642 Acquired customer base 21,856 Acquired database technology 4,076 Acquired building photography 2,425 Deferred income taxes, net 9,290 Other assets and liabilities (849 ) Fair value of identifiable net assets acquired $ 172,727 The net assets of Apartment Finder were recorded at their estimated fair value. In valuing acquired assets and liabilities, fair value estimates were based on, but were not limited to, future expected cash flows, market rate assumptions for contractual obligations, and appropriate discount rates. The acquired customer base for the acquisition consisted of three distinct intangible assets, is composed of acquired customer contracts and the related customer relationships, and has a weighted average estimated useful life of ten years . The acquired database technology had an estimated useful life of five months due to the Company's intent to replace the acquired database technology in 2015, which it did in December 2015. The acquired trade names and other intangible assets have a weighted average estimated useful life of nine years . The acquired building photography had an estimated useful life of five months . Amortization of the acquired customer base is recognized on an accelerated basis related to the expected economic benefit of the intangible asset, while amortization of the acquired database technology, acquired building photography and acquired trade names and other intangible assets is recognized on a straight-line basis over their respective estimated useful lives. Goodwill recorded in connection with this acquisition is not amortized, but is subject to annual impairment tests. The $108 million of goodwill recorded as part of the acquisition is associated with the Company's North America operating segment. None of the goodwill recognized is expected to be deductible for income tax purposes in future periods. 3. ACQUISITION — (CONTINUED) Goodwill is calculated as the excess of the consideration transferred over the net assets recognized and represents the future economic benefits arising from other assets acquired that could not be individually identified and separately recognized. Specifically, the goodwill recorded as part of the Apartment Finder acquisition includes but is not limited to: (i) the expected synergies and other benefits that the Company believes will result from combining its operations with Apartment Finder's operations; and (ii) any intangible assets that do not qualify for separate recognition, such as the assembled workforce.

INVESTMENTS

INVESTMENTS	9 Months Ended
	Sep. 30, 2016
Investments, Debt and Equity Securities [Abstract]
INVESTMENTS	INVESTMENTS The Company determines the appropriate classification of debt and equity investments at the time of purchase and re-evaluates such designation as of each balance sheet date. The Company considers all of its investments to be available-for-sale. The Company's investments consist of short-term and long-term variable rate debt instruments with an auction reset feature, referred to as auction rate securities (“ARS”). Available-for-sale investments with contractual maturities of one year or less are classified as short-term in the Company's condensed consolidated balance sheets. Investments are carried at fair value. Scheduled maturities of investments classified as available-for-sale as of September 30, 2016 are as follows (in thousands): Maturity Fair Value Due: October 1, 2016 — September 30, 2017 $ 1,171 October 1, 2017 — September 30, 2021 — October 1, 2021 — September 30, 2026 — After September 30, 2026 9,911 Available-for-sale investments $ 11,082 The Company had no realized gains on its investments for each of the three and nine months ended September 30, 2016 and 2015 . The Company had no realized losses on its investments for each of the three and nine months ended September 30, 2016 and 2015 . Realized gains and losses from the sale of available-for-sale securities are determined on a specific-identification basis. Changes in unrealized holding gains and losses, net of the related tax effect, on available-for-sale securities are excluded from earnings and are reported as a separate component of accumulated other comprehensive loss in stockholders’ equity until realized. A decline in market value of any available-for-sale security below cost that is deemed to be other-than-temporary results in a reduction in carrying amount to fair value. The impairment is charged to earnings and a new cost basis for the security is established. Dividend and interest income are recognized when earned. As of September 30, 2016 , the amortized cost basis and fair value of investments classified as available-for-sale were as follows (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Auction rate securities $ 11,242 $ 728 $ (888 ) $ 11,082 Available-for-sale investments $ 11,242 $ 728 $ (888 ) $ 11,082 As of December 31, 2015 , the amortized cost basis and fair value of investments classified as available-for-sale were as follows (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Auction rate securities $ 15,942 $ 610 $ (1,045 ) $ 15,507 Available-for-sale investments $ 15,942 $ 610 $ (1,045 ) $ 15,507 4. INVESTMENTS — (CONTINUED) The unrealized losses on the Company’s investments as of September 30, 2016 and December 31, 2015 were generated primarily from changes in interest rates and ARS that failed to settle at auction, due to adverse conditions in the global credit markets. The losses are considered temporary, as the contractual terms of these investments do not permit the issuer to settle the security at a price less than the amortized cost of the investment. Because the Company does not intend to sell these instruments and it is not more likely than not that the Company will be required to sell these instruments prior to anticipated recovery, which may be at maturity, the Company does not consider these investments to be other-than-temporarily impaired as of September 30, 2016 and December 31, 2015 . See Note 5 for further discussion of the fair value of the Company’s financial assets. The components of the Company’s investments in an unrealized loss position for twelve months or longer were as follows (in thousands): September 30, December 31, Aggregate Fair Value Gross Unrealized Losses Aggregate Fair Value Gross Unrealized Losses Auction rate securities $ 9,911 $ (888 ) $ 14,455 $ (1,045 ) Investments in an unrealized loss position $ 9,911 $ (888 ) $ 14,455 $ (1,045 ) The Company did not have any investments in an unrealized loss position for less than twelve months as of September 30, 2016 and December 31, 2015 .

FAIR VALUE

FAIR VALUE	9 Months Ended
	Sep. 30, 2016
Fair Value Disclosures [Abstract]
FAIR VALUE	FAIR VALUE Fair value is defined as the price that would be received in the sale of an asset or paid to transfer a liability in an orderly transaction between market participants. There is a three-tier fair value hierarchy, which categorizes the inputs used in measuring fair value. These tiers include: Level 1, defined as observable inputs such as quoted prices in active markets for identical assets or liabilities; Level 2, defined as inputs other than quoted prices in active markets that are either directly or indirectly observable; and Level 3, defined as unobservable inputs for which little or no market data exists, therefore requiring an entity to develop its own assumptions. The following table represents the Company's fair value hierarchy for its financial assets (cash, cash equivalents and investments) measured at fair value on a recurring basis as of September 30, 2016 (in thousands): Level 1 Level 2 Level 3 Total Assets: Cash $ 338,510 $ — $ — $ 338,510 Money market funds 175,328 — — 175,328 Commercial paper 8,261 — — 8,261 Auction rate securities — — 11,082 11,082 Total assets measured at fair value $ 522,099 $ — $ 11,082 $ 533,181 The following table represents the Company's fair value hierarchy for its financial assets (cash, cash equivalents and investments) measured at fair value on a recurring basis as of December 31, 2015 (in thousands): Level 1 Level 2 Level 3 Total Assets: Cash $ 405,597 $ — $ — $ 405,597 Money market funds 5,043 — — 5,043 Commercial paper 11,178 — — 11,178 Auction rate securities — — 15,507 15,507 Total assets measured at fair value $ 421,818 $ — $ 15,507 $ 437,325 5. FAIR VALUE — (CONTINUED) The Company’s Level 3 assets consist of ARS, whose underlying assets are primarily student loan securities supported by guarantees from the Federal Family Education Loan Program (“FFELP”) of the U.S. Department of Education. The following tables summarize changes in fair value of the Company’s Level 3 assets for the three and nine months ended September 30, 2016 and 2015 (in thousands): Three Months Ended Nine Months Ended 2016 2015 2016 2015 Balance at beginning of period $ 11,036 $ 16,049 $ 15,507 $ 17,151 Decrease in unrealized loss included in accumulated other comprehensive loss 46 8 275 256 Settlements — (550 ) (4,700 ) (1,900 ) Balance at end of period $ 11,082 $ 15,507 $ 11,082 $ 15,507 The following table summarizes changes in fair value of the Company’s Level 3 assets from December 31, 2014 to September 30, 2016 (in thousands): Auction Rate Securities Balance at December 31, 2014 $ 17,151 Decrease in unrealized loss included in accumulated other comprehensive loss 256 Settlements (1,900 ) Balance at December 31, 2015 15,507 Decrease in unrealized loss included in accumulated other comprehensive loss 275 Settlements (4,700 ) Balance at September 30, 2016 $ 11,082 ARS are variable rate debt instruments whose interest rates are reset approximately every 28 days . The majority of the underlying securities have contractual maturities greater than twenty years . The ARS are recorded at fair value. As of September 30, 2016 , the Company held ARS with $12 million par value, all of which failed to settle at auction. The majority of these investments are of high credit quality with AAA credit ratings and are primarily student loan securities supported by guarantees from the FFELP of the U.S. Department of Education. The Company may not be able to liquidate and fully recover the carrying value of the ARS in the near term. As a result, most of these securities are classified as long-term investments in the Company’s condensed consolidated balance sheet as of September 30, 2016 . ARS with contractual maturities of one year or less are classified as short-term investments in the Company's condensed consolidated balance sheets. See Note 4 for further discussion of the scheduled maturities of investments classified as available-for-sale. While the Company continues to earn interest on its ARS investments at the contractual rate, these investments are not currently actively trading and therefore do not currently have a readily determinable market value. The estimated fair value of the ARS no longer approximates par value. The Company used a discounted cash flow model to determine the estimated fair value of its investment in ARS as of September 30, 2016 . The assumptions used in preparing the discounted cash flow model include estimates for interest rates, credit spreads, timing and amount of contractual cash flows, liquidity risk premiums, expected holding periods and default risk. The Company updates the discounted cash flow model on a quarterly basis to reflect any changes in the assumptions used in the model and settlements of ARS investments that occurred during the period. The only significant unobservable input in the discounted cash flow model is the discount rate. The discount rate used represents the Company's estimate of the yield expected by a market participant from the ARS investments. The weighted average discount rate used in the discounted cash flow model as of September 30, 2016 and December 31, 2015 was approximately 6% and 5% , respectively. Selecting another discount rate within the range used in the discounted cash flow model would not result in a significant change to the fair value of the ARS. 5. FAIR VALUE — (CONTINUED) Based on this assessment of fair value, as of September 30, 2016 , the Company determined there was a net decline in the fair value of its ARS investments of approximately $160,000 . The decline was deemed to be a temporary impairment and recorded as an unrealized loss in accumulated other comprehensive loss in stockholders’ equity. In addition, while a majority of the ARS are currently rated AAA, if the issuers are unable to successfully close future auctions and/or their credit ratings deteriorate, the Company may be required to record additional unrealized losses in accumulated other comprehensive loss or an other-than-temporary impairment charge to earnings on these investments. Concentration of Credit Risk and Financial Instruments The Company performs ongoing credit evaluations of its customers’ financial condition and generally does not require that its customers’ obligations to the Company be secured. The Company maintains reserves for estimated inherent credit losses, and such losses have been within management’s expectations. The large size and widespread nature of the Company’s customer base and the Company’s lack of dependence on any individual customer mitigates the risk of nonpayment of the Company’s accounts receivable. The carrying amount of the accounts receivable approximates the net realizable value. The carrying value of accounts receivable, accounts payable, accrued expenses and long-term debt approximates fair value.

GOODWILL

GOODWILL	9 Months Ended
	Sep. 30, 2016
Goodwill [Abstract]
GOODWILL	GOODWILL The changes in the carrying amount of goodwill by operating segment consist of the following (in thousands): North America International Total Goodwill, December 31, 2014 $ 1,114,363 $ 24,442 $ 1,138,805 Acquisition 112,947 2,400 115,347 Effect of foreign currency translation — (1,207 ) (1,207 ) Goodwill, December 31, 2015 1,227,310 25,635 1,252,945 Acquisitions 467 5,933 6,400 Effect of foreign currency translation — (2,992 ) (2,992 ) Goodwill, September 30, 2016 $ 1,227,777 $ 28,576 $ 1,256,353 The Company recorded goodwill of approximately $108 million in connection with the June 1, 2015 acquisition of Apartment Finder and recorded goodwill of approximately $2 million in connection with the July 1, 2015 acquisition of the assets of Belbex Corporate, S.L., a commercial real estate information provider operating in Madrid, Spain. Additionally, the Company recorded goodwill of approximately $5 million during the year ended December 31, 2015 and approximately $467,000 for the nine months ended September 30, 2016 , in connection with the acquisition of certain assets related to the business operations of Apartment Finder's independent distributors within various markets. Finally, the Company recorded goodwill of approximately $6 million in connection with the May 3, 2016 acquisition of Thomas Daily GmbH (“Thomas Daily”), a commercial real estate news and information provider operating in Freiburg, Germany. The purchase accounting for the acquisition of Thomas Daily is preliminary, subject to the completion of the accounting for certain tax related items.

INTANGIBLE ASSETS

INTANGIBLE ASSETS	9 Months Ended
	Sep. 30, 2016
Intangible Assets, Net (Excluding Goodwill) [Abstract]
INTANGIBLE ASSETS	INTANGIBLE ASSETS Intangible assets consist of the following (in thousands, except amortization period data): September 30, December 31, Weighted- Average Amortization Period (in years) Capitalized product development cost $ 2,275 $ 2,243 4 Accumulated amortization (2,205 ) (2,172 ) Capitalized product development cost, net 70 71 Building photography 17,375 17,677 4 Accumulated amortization (16,246 ) (15,875 ) Building photography, net 1,129 1,802 Acquired database technology 78,332 77,905 5 Accumulated amortization (69,870 ) (62,818 ) Acquired database technology, net 8,462 15,087 Acquired customer base 221,385 221,409 10 Accumulated amortization (145,859 ) (129,782 ) Acquired customer base, net 75,526 91,627 Acquired trade names and other intangible assets 153,736 153,910 13 Accumulated amortization (31,810 ) (24,179 ) Acquired trade names and other intangible assets, net 121,926 129,731 Intangible assets, net $ 207,113 $ 238,318 In February 2015, as a result of the Company's product development efforts, it launched an improved Apartments.com website with a cleaner look, information about actual rental availabilities, rents and other fees, and better search functionality. In conjunction with the launch, the Company ceased using the database technology acquired in the acquisition of Apartments.com. The Company evaluated the acquired database technology for impairment during the first quarter of 2015 and determined that the carrying value of the acquired database technology was impaired as the Company had ceased using the asset. The Company recorded an impairment charge of approximately $1 million in cost of revenues in the condensed consolidated statements of operations within the Company's North America operating segment for the nine months ended September 30, 2015 . In June 2015, following the June 1, 2015 acquisition of Apartment Finder, the Company decided to cease providing certain Apartment Finder services. Additionally, in June 2015, the Company decided to cease development work related to a development project within Apartment Finder. The Company evaluated the acquired customer base and acquired database technology for impairment during the second quarter of 2015 and, based on that evaluation, determined that the customer base and database technology assets associated with the ceased services and development work were impaired as they were not expected to provide any economic benefit to the Company. The Company recorded an impairment charge of approximately $1 million , most of which was recorded in general and administrative expenses in the condensed consolidated statements of operations within the Company's North America operating segment for the nine months ended September 30, 2015 . 7. INTANGIBLE ASSETS — (CONTINUED) Intangible assets are reviewed for impairment at least annually and more frequently whenever events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. During the first quarter of 2016, the Company determined that the acquired trade names recorded in connection with the LoopNet acquisition on April 30, 2012 should be reclassified from an indefinite-lived intangible asset to a definite-lived intangible asset due to work being performed to integrate the backend systems of LoopNet and CoStar, which may result in a future re-branding effort if aspects of the two services are ultimately combined. The Company estimated the fair value of the LoopNet trade names using the relief from royalty method and concluded that no impairment existed as of March 31, 2016. The Company estimated a useful life of fifteen years for the LoopNet trade names, which are being amortized on a straight-line basis.

LONG-TERM DEBT

LONG-TERM DEBT	9 Months Ended
	Sep. 30, 2016
Long-term Debt, Current and Noncurrent [Abstract]
LONG-TERM DEBT	LONG-TERM DEBT On April 1, 2014 (the “Closing Date”), the Company entered into the 2014 Credit Agreement by and among the Company, as Borrower, CoStar Realty Information, Inc., as Co-Borrower, the Lenders from time to time party thereto and JPMorgan Chase Bank, N.A., as Administrative Agent. The 2014 Credit Agreement provides for a $400 million term loan facility and a $225 million revolving credit facility, each with a term of five years . The proceeds of the term loan facility and the initial borrowing of $150 million under the revolving credit facility on the Closing Date were used to refinance the 2012 Credit Agreement, including related fees and expenses, and to pay a portion of the consideration and transaction costs related to the acquisition of Apartments.com. The undrawn proceeds of the revolving credit facility are available for the Company's working capital needs and other general corporate purposes. During June 2014, the Company repaid the $150 million initial borrowing under the revolving credit facility. The carrying value of the term loan facility approximates fair value and can be estimated through Level 3 unobservable inputs using a valuation technique based on expected cash flows discounted using the current credit-adjusted risk-free rate, which approximates the rate of interest on the term loan facility at origination. Effective April 1, 2014, the Company terminated the 2012 Credit Agreement and repaid all amounts outstanding thereunder, which amounts totaled $149 million . The Company evaluated the execution of the 2014 Credit Agreement and termination of the 2012 Credit Agreement and determined that the transactions did not qualify as an extinguishment of debt because the change in the present value of future cash flows between the initial term loan facility under the 2012 Credit Agreement and the new term loan facility under the 2014 Credit Agreement was not considered a substantial modification. The revolving credit facility includes a subfacility for swingline loans of up to $10 million , and up to $10 million of the revolving credit facility is available for the issuance of letters of credit. The term loan facility will amortize in quarterly installments in amounts resulting in an annual amortization of 5% during each of the first, second and third years, 10% during the fourth year and 15% during the fifth year after the Closing Date, with the remainder payable at final maturity. The loans under the 2014 Credit Agreement bear interest, at the Company's option, either (i) during any interest period selected by the Company, at the London interbank offered rate for deposits in U.S. dollars with a maturity comparable to such interest period, adjusted for statutory reserves (“LIBOR”), plus an initial spread of 2% per annum, subject to adjustment based on the First Lien Secured Leverage Ratio (as defined in the 2014 Credit Agreement) of the Company, or (ii) at the greatest of (x) the prime rate from time to time announced by JPMorgan Chase Bank, N.A., (y) the federal funds effective rate plus 0.5% and (z) LIBOR for a one-month interest period plus 1% , plus an initial spread of 1% per annum, subject to adjustment based on the First Lien Secured Leverage Ratio of the Company. If an event of default occurs under the 2014 Credit Agreement, the interest rate on overdue amounts will increase by 2% per annum. The obligations under the 2014 Credit Agreement are guaranteed by all material subsidiaries of the Company and are secured by a lien on substantially all of the assets of the Company and those of its material subsidiaries, in each case subject to certain exceptions, pursuant to security and guarantee documents entered into on the Closing Date. The 2014 Credit Agreement requires the Company to maintain (i) a First Lien Secured Leverage Ratio (as defined in the 2014 Credit Agreement) not exceeding 3.5 to 1.0 during the three months ended September 30, 2016 , and each full fiscal quarter thereafter and (ii) after the incurrence of additional indebtedness under certain specified exceptions in the 2014 Credit Agreement, a Total Leverage Ratio (as defined in the 2014 Credit Agreement) not exceeding 4.5 to 1.0 during the three months ended September 30, 2016 , and each full fiscal quarter thereafter. The 2014 Credit Agreement also includes other covenants, including covenants that, subject to certain exceptions, restrict the ability of the Company and its subsidiaries to (i) incur additional indebtedness, (ii) create, incur, assume or permit to exist any liens, (iii) enter into mergers, consolidations or similar transactions, (iv) make investments and acquisitions, (v) make certain dispositions of assets, (vi) make dividends, distributions and prepayments of certain indebtedness, and (vii) enter into certain transactions with affiliates. The Company was in compliance with the covenants in the 2014 Credit Agreement as of September 30, 2016 . 8. LONG-TERM DEBT — (CONTINUED) In connection with obtaining the term loan facility and revolving credit facility pursuant to the 2014 Credit Agreement, the Company incurred approximately $10 million in debt issuance costs as of April 1, 2014, which along with the unamortized debt issuance cost from the 2012 Credit Agreement, were capitalized and are amortized as interest expense over the term of the 2014 Credit Agreement using the effective interest method. As of September 30, 2016 and December 31, 2015 , no amounts were outstanding under the revolving credit facility. Total interest expense for the term loan facility and revolving credit facility was approximately $2 million for each of the three months ended September 30, 2016 and 2015 . Total interest expense for the term loan facility and revolving credit facility was approximately $7 million for each of the nine months ended September 30, 2016 and 2015 . Interest expense included amortized debt issuance costs of approximately $797,000 and $830,000 for the three months ended September 30, 2016 and 2015 , respectively. Interest expense included amortized debt issuance costs of approximately $2 million for each of the nine months ended September 30, 2016 and 2015 . Total interest paid for the term loan facility and revolving credit facility was approximately $2 million for each of the three months ended September 30, 2016 and 2015 . Total interest paid for the term loan facility and revolving credit facility was approximately $5 million for each of the nine months ended September 30, 2016 and 2015 . The following table represents the Company's long-term debt (in thousands): September 30, December 31, Term loan facility $ 345,000 $ 365,000 Debt issuance costs, net (7,481 ) (9,888 ) Total debt 337,519 355,112 Current maturities of long-term debt (25,000 ) (20,000 ) Current debt issuance costs, net 3,175 3,254 Total long-term debt, less current portion $ 315,694 $ 338,366

INCOME TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 2016
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The income tax provision for the nine months ended September 30, 2016 and 2015 reflects an effective tax rate of approximately 39% and 14% , respectively. The change in the effective tax rate is primarily due to a larger impact of nondeductible expenses during the nine months ended September 30, 2015 and a change in local tax law that occurred during the first quarter of 2015.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2016
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES The Company leases office facilities and office equipment under various non-cancelable operating leases. The leases contain various renewal options. On April 1, 2014, the Company entered into the 2014 Credit Agreement. The 2014 Credit Agreement provides for a $400 million term loan facility and a $225 million revolving credit facility, each with a term of five years . See Note 8 for additional information regarding the term loan facility and revolving credit facility. Currently, and from time to time, the Company is involved in litigation incidental to the conduct of its business. In accordance with GAAP, the Company records a provision for a liability when it is both probable that a liability has been incurred and the amount can be reasonably estimated. At the present time, while it is reasonably possible that an unfavorable outcome may occur as a result of one or more of the Company’s current litigation matters, management has concluded that it is not probable that a loss has been incurred in connection with the Company’s current litigation. In addition, the Company is unable to estimate the possible loss or range of loss that could result from an unfavorable outcome in the Company’s current litigation and accordingly, the Company has not recognized any liability in the condensed consolidated financial statements for unfavorable results, if any. Legal defense costs are expensed as incurred.

SEGMENT REPORTING

SEGMENT REPORTING	9 Months Ended
	Sep. 30, 2016
Segment Reporting [Abstract]
SEGMENT REPORTING	SEGMENT REPORTING Segment Information The Company manages its business geographically in two operating segments, with the primary areas of measurement and decision-making being North America, which includes the U.S. and Canada, and International, which includes the U.K., Spain, Germany and France. The Company and its subsidiaries' subscription-based services consist primarily of information, analytics and online marketplace services offered over the Internet to commercial real estate industry and related professionals. The Company’s subscription-based information services consist primarily of CoStar Suite ® services. CoStar Suite is sold as a platform of service offerings consisting of CoStar Property Professional ® , CoStar COMPS Professional ® and CoStar Tenant ® and through the Company's mobile application, CoStar Go ® . CoStar Suite is the Company’s primary service offering in the North America and International operating segments. Management relies on an internal management reporting process that provides revenue and operating segment net income (loss) before interest, income taxes, depreciation and amortization (“EBITDA”). Management believes that operating segment EBITDA is an appropriate measure for evaluating the operational performance of the Company’s operating segments. EBITDA is used by management to internally measure operating and management performance and to evaluate the performance of the business. However, this measure should be considered in addition to, not as a substitute for or superior to, income from operations or other measures of financial performance prepared in accordance with GAAP. Summarized information by operating segment consists of the following (in thousands): Three Months Ended Nine Months Ended 2016 2015 2016 2015 Revenues North America $ 205,637 $ 182,556 $ 598,757 $ 500,059 International External customers 7,074 6,522 20,562 18,696 Intersegment revenue 3 4 24 25 Total International revenue 7,077 6,526 20,586 18,721 Intersegment eliminations (3 ) (4 ) (24 ) (25 ) Total revenues $ 212,711 $ 189,078 $ 619,319 $ 518,755 EBITDA North America $ 56,305 $ 20,993 $ 148,296 $ 32,816 International 1,371 1,096 2,761 2,124 Total EBITDA $ 57,676 $ 22,089 $ 151,057 $ 34,940 The reconciliation of net income (loss) to EBITDA consists of the following (in thousands): Three Months Ended Nine Months Ended 2016 2015 2016 2015 Net income (loss) $ 23,201 $ (5,362 ) $ 55,498 $ (26,455 ) Purchase amortization in cost of revenues 5,736 9,964 17,119 22,887 Purchase amortization in operating expenses 5,550 7,153 17,602 21,260 Depreciation and other amortization 6,794 5,403 18,320 14,860 Interest income (344 ) (42 ) (587 ) (473 ) Interest expense 2,498 2,363 7,462 7,060 Income tax expense (benefit), net 14,241 2,610 35,643 (4,199 ) EBITDA $ 57,676 $ 22,089 $ 151,057 $ 34,940 11. SEGMENT REPORTING — (CONTINUED) Segment Information — (Continued) Intersegment revenue recorded was attributable to services performed for the Company’s wholly owned subsidiary, CoStar Portfolio Strategy by Grecam S.A.S. (“Grecam”), a wholly owned subsidiary of CoStar Limited, the Company’s wholly owned U.K. holding company. North America EBITDA includes an allocation of approximately $70,000 and $225,000 for the three months ended September 30, 2016 and 2015 , respectively. North America EBITDA includes an allocation of approximately $379,000 and $763,000 for the nine months ended September 30, 2016 and 2015 , respectively. This allocation represents costs incurred for International employees involved in development activities of the Company’s North America operating segment. International EBITDA includes a corporate allocation of approximately $113,000 and $74,000 for the three months ended September 30, 2016 and 2015 , respectively. International EBITDA includes a corporate allocation of approximately $246,000 and $200,000 for the nine months ended September 30, 2016 and 2015 , respectively. This corporate allocation represents costs incurred for North America employees involved in management and expansion activities of the Company’s International operating segment. 11. SEGMENT REPORTING — (CONTINUED) Segment Information — (Continued) Summarized information by operating segment consists of the following (in thousands): September 30, December 31, Property and equipment, net North America $ 83,415 $ 86,191 International 1,951 2,120 Total property and equipment, net $ 85,366 $ 88,311 Goodwill North America $ 1,227,777 $ 1,227,310 International 28,576 25,635 Total goodwill $ 1,256,353 $ 1,252,945 Assets North America $ 2,205,725 $ 2,130,202 International 45,990 41,370 Total operating segment assets $ 2,251,715 $ 2,171,572 Reconciliation of operating segment assets to total assets Total operating segment assets $ 2,251,715 $ 2,171,572 Investment in subsidiaries (18,344 ) (18,344 ) Intersegment receivables (80,784 ) (73,657 ) Total assets $ 2,152,587 $ 2,079,571 Liabilities North America $ 523,844 $ 525,566 International 71,094 72,544 Total operating segment liabilities $ 594,938 $ 598,110 Reconciliation of operating segment liabilities to total liabilities Total operating segment liabilities $ 594,938 $ 598,110 Intersegment payables (61,049 ) (62,319 ) Total liabilities $ 533,889 $ 535,791 11. SEGMENT REPORTING — (CONTINUED) Revenues by Services The Company provides information, analytics and online marketplaces to the commercial real estate industry. The revenue by type of service consists of the following (in thousands): Three Months Ended Nine Months Ended 2016 2015 2016 2015 Information and analytics CoStar Suite (1) $ 103,261 $ 91,350 $ 301,969 $ 266,931 Information services (2) 19,486 19,126 58,336 56,415 Online marketplaces Multifamily (3) 57,654 49,312 164,752 110,187 Commercial property and land (4) 32,310 29,290 94,262 85,222 Total revenues $ 212,711 $ 189,078 $ 619,319 $ 518,755 (1) CoStar Suite is comprised of CoStar Property Professional, CoStar COMPS Professional, CoStar Tenant; CoStar Market Analytics; and CoStar Portfolio Strategy. (2) Information services is comprised of LoopNet Premium Searcher; CoStar Real Estate Manager; CoStar Risk Analytics COMPASS; CoStar Investment Analysis Portfolio Maximizer; CoStar Investment Analysis Request; CoStar Brokerage Applications; PROPEX; Grecam; Belbex and Thomas Daily. (3) Multifamily is comprised of Apartments.com, ApartmentFinder.com and ApartmentHomeLiving.com. (4) Commercial property and land is comprised of LoopNet Premium Lister; LoopLink; CoStar Advertising; BizBuySell and BizQuest; LandsofAmerica and LandAndFarm; and CoStar Private Sale Network.

SUMMARY OF SIGNIFICANT ACCOUN18

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
	Sep. 30, 2016
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Accounting policies are consistent for each operating segment.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company evaluates its estimates and assumptions, including those related to revenue recognition, allowance for doubtful accounts, useful lives of property and equipment and intangible assets, recoverability of long-lived assets and intangible assets with definite lives, goodwill, income taxes, fair value of equity instruments, fair value of auction rate securities, accounting for business combinations and contingencies, among others. The Company bases these estimates on historical and anticipated results, trends, and various other assumptions that it believes are reasonable, including assumptions as to future events. These estimates form the basis for making judgments about the carrying values of assets and liabilities and recorded revenue and expenses. Actual results could differ from these estimates.
Reclassifications	Reclassifications Certain previously reported amounts in the condensed consolidated balance sheets as of December 31, 2015 have been reclassified to conform to the Company's current presentation to reflect current income taxes payable separately, which was previously included in accrued expenses.
Advertising Costs	Advertising Costs The Company expenses advertising costs as incurred. Advertising costs include e-commerce, television, radio, print and other media advertising.
Foreign Currency Translation	Foreign Currency Translation The Company’s functional currency in its foreign locations is the local currency. Assets and liabilities are translated into U.S. dollars using the exchange rates as of the balance sheet dates. Revenues, expenses, gains and losses are translated at the average exchange rates in effect during each period. Gains and losses resulting from translation are included in accumulated other comprehensive loss. Net gains or losses resulting from foreign currency exchange transactions are included in the condensed consolidated statements of operations.
Net Income (Loss) Per Share	Net Income (Loss) Per Share Net income (loss) per share is computed by dividing net income (loss) by the weighted average number of common shares outstanding during the period on a basic and diluted basis. The Company’s potentially dilutive securities include stock options and restricted stock. Diluted net income (loss) per share considers the impact of potentially dilutive securities except in periods in which there is a net loss, as the inclusion of the potentially dilutive common shares would have an anti-dilutive effect. Stock options to purchase approximately 89,000 and 184,000 shares that were outstanding for the three and nine months ended September 30, 2016 , respectively, were not included in the computation of diluted net income per share because the inclusion would have an anti-dilutive effect. The Company did not consider the impact of potentially dilutive securities for the three and nine months ended September 30, 2015 when calculating the diluted net loss per share because the inclusion of the potentially dilutive common shares would have an anti-dilutive effect. Shares underlying restricted common stock awards that vest based on Company performance and service conditions, that have not been achieved as of the end of the period are not included in the computation of basic or diluted earnings per share.
Stock-Based Compensation	Stock-Based Compensation Equity instruments issued in exchange for employee services are accounted for using a fair-value based method and the fair value of such equity instruments is recognized as expense in the condensed consolidated statements of operations. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED) Stock-Based Compensation — (Continued) Stock-based compensation expense is measured at the grant date of the stock-based awards that vest over set time periods based on their fair values, and is recognized on a straight line basis as expense over the vesting periods of the awards, net of an estimated forfeiture rate. For equity instruments that vest based on performance, the Company assesses the probability of the achievement of the performance conditions at the end of each reporting period, or more frequently based upon the occurrence of events that may change the probability of whether the performance conditions would be met. If the Company's initial estimates of the achievement of the performance conditions change, the related stock-based compensation expense and timing of recognition may fluctuate from period to period based on those estimates. For equity instruments that vest based on a performance condition and a market condition, the Company estimates the fair value of each equity instrument granted on the date of grant using a Monte-Carlo simulation model. This pricing model uses multiple simulations to evaluate the probability of achieving the market condition to calculate the fair value of the awards. Stock-based compensation expense is updated based on the expected achievement of the related performance conditions at the end of each reporting period. If the performance conditions are not met, no stock-based compensation expense will be recognized, and any previously recognized stock-based compensation expense will be reversed. Cash flows resulting from excess tax benefits are classified as part of cash flows from operating and financing activities. Excess tax benefits represent tax benefits for stock-based compensation in excess of the associated deferred tax asset for such equity compensation recorded as an increase to stockholders' equity.
Debt Issuance Costs	Debt Issuance Costs Costs incurred in connection with the issuance of long-term debt are capitalized and amortized as interest expense over the term of the related debt using the effective interest method. These amounts are reflected in the consolidated balance sheets as direct deductions from a combination of the current and long-term portions of debt. Upon a refinancing, previously capitalized debt issuance costs are expensed and included in loss on extinguishment of debt if the Company determines that there has been a substantial modification of the related debt. If the Company determines that there has not been a substantial modification of the related debt, any previously capitalized debt issuance costs are amortized as interest expense over the term of the new debt instrument using the effective interest method.
Business Combinations	Business Combinations The Company allocates the purchase consideration to the tangible assets acquired, liabilities assumed and intangible assets acquired based on their estimated fair values. The excess of the fair value of purchase consideration over the fair values of these identifiable assets and liabilities is recorded as goodwill. Such valuations require management to make significant estimates and assumptions, especially with respect to intangible assets. Significant estimates in valuing certain intangible assets include, but are not limited to, future expected cash flows from acquired customer bases, acquired database technology, and acquired trade names from a market participant's perspective, useful lives and discount rates. During the measurement period, the Company may record adjustments to the assets acquired and liabilities assumed. Any adjustments to provisional amounts that are identified during the measurement period are recorded in the reporting period in which the adjustment amounts are determined. Upon the conclusion of the measurement period, any subsequent adjustments are recorded to earnings.
Recent Accounting Pronouncements	Recent Accounting Pronouncements There have been no developments to the Recent Accounting Pronouncements discussion included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2015 , including the expected dates of adoption and estimated effects on the Company’s condensed consolidated financial statements, except for the following: 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED) Recent Accounting Pronouncements — (Continued) In May 2014, the Financial Accounting Standards Board (“FASB”) and International Accounting Standards Board (“IASB”) jointly issued a new revenue recognition standard that is designed to improve financial reporting by creating common recognition guidance for GAAP and International Financial Reporting Standards (“IFRS”). This guidance provides a robust framework for addressing revenue issues, improves the comparability of revenue recognition practices across industries, provides useful information to users of financial statements through improved disclosure requirements and simplifies the presentation of financial statements. The core principle of the guidance is that an entity should recognize revenue to depict the transfer of promised goo ds or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. From March to May of 2016, amendments to the new revenue recognition standard were issued to clarify numerous accounting topics, including, but not limited to (i) the implementation guidance on principal versus agent considerations, (ii) the identification of performance obligations, (iii) the licensing implementation guidance, (iv) the objective of the collectability criterion and (v) the application of the variable consideration guidance and modified retrospective transition method. This guidance permits the use of either a full retrospective method or a modified retrospective approach. The modified retrospective approach would be applied only to the most current period presented along with a cumulative-effect adjustment at the date of adoption. This guidance will be effective for annual reporting periods beginnin g after December 15, 2017, although companies may adopt the standard as early as annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. The Company has not yet determined when it will adopt the standard or selected a transition method and is currently evaluating the impact this guidance will have on its financial statements and related disclosures. In February 2016, the FASB issued authoritative lease guidance to increase transparency and comparability among organizations. The guidance requires a company to recognize lease assets and lease liabilities on the balance sheet as well as disclose key information about leasing arrangements. This guidance is effective on a modified retrospective basis for annual reporting periods beginning after December 15, 2018, including interim periods within that reporting period. Early application is permitted. The Company is currently evaluating the impact this guidance will have on its financial statements and related disclosures. In March 2016, the FASB issued authoritative guidance to simplify several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification of share-based payment transactions on the statement of cash flows. The guidance requires a company to (i) recognize all excess tax benefits and tax deficiencies as income tax expense or benefit in the statement of operations using a prospective transition method, (ii) recognize excess tax benefits in the current period regardless of whether the benefit reduces taxes payable using a modified retrospective transition method, and (iii) classify all excess tax benefits as operating activities within the statement of cash flows using either a prospective transition method or a retrospective transition method. The guidance also allows a company to (i) elect whether to estimate the number of awards expected to vest or account for forfeitures when they occur, and (ii) withhold up to the maximum statutory tax rate in the applicable jurisdiction for awards, both of which should be applied using a modified retrospective transition method. Finally, the guidance requires a company to classify the cash paid by an employer when directly withholding shares for tax withholding purposes as a financing activity within the statement of cash flows using a retrospective transition method. This guidance is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. Early application is permitted. The Company is currently evaluating the impact this guidance will have on its financial statements and related disclosures. In June 2016, the FASB issued authoritative guidance designed to provide financial statement users with more information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. When determining such expected credit losses, the guidance requires companies to apply a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. This guidance is effective on a modified retrospective basis for annual reporting periods beginning after December 15, 2019, including interim periods within that reporting period. C ompanies may adopt the standard as early as annual reporting periods beginning after December 15, 2018 . The Company is currently evaluating the impact this guidance will have on its financial statements and related disclosures. 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED) Recent Accounting Pronouncements — (Continued) In August 2016, the FASB issued authoritative guidance designed to reduce the existing diversity in how certain cash receipts and cash payments are presented and classified in the consolidated statements of cash flows. This guidance is effective on a retrospective basis for annual reporting periods beginning after December 15, 2017, including interim periods within that reporting period. Early application is permitted. This guidance is not expected to have a material impact on the Company's consolidated statements of cash flows and related disclosures.

ACQUISITION (Policies)

ACQUISITION (Policies)	9 Months Ended
	Sep. 30, 2016
Business Acquisition [Line Items]
Acquisition	Business Combinations The Company allocates the purchase consideration to the tangible assets acquired, liabilities assumed and intangible assets acquired based on their estimated fair values. The excess of the fair value of purchase consideration over the fair values of these identifiable assets and liabilities is recorded as goodwill. Such valuations require management to make significant estimates and assumptions, especially with respect to intangible assets. Significant estimates in valuing certain intangible assets include, but are not limited to, future expected cash flows from acquired customer bases, acquired database technology, and acquired trade names from a market participant's perspective, useful lives and discount rates. During the measurement period, the Company may record adjustments to the assets acquired and liabilities assumed. Any adjustments to provisional amounts that are identified during the measurement period are recorded in the reporting period in which the adjustment amounts are determined. Upon the conclusion of the measurement period, any subsequent adjustments are recorded to earnings.
Apartment Finder [Member]
Business Acquisition [Line Items]
Acquisition	The Company applied the acquisition method to account for the Apartment Finder transaction, which requires that, among other things, assets acquired and liabilities assumed be recorded at their fair values as of the acquisition date.

INVESTMENTS (Policies)

INVESTMENTS (Policies)	9 Months Ended
	Sep. 30, 2016
Investments, Debt and Equity Securities [Abstract]
Investments	The Company determines the appropriate classification of debt and equity investments at the time of purchase and re-evaluates such designation as of each balance sheet date. The Company considers all of its investments to be available-for-sale. The Company's investments consist of short-term and long-term variable rate debt instruments with an auction reset feature, referred to as auction rate securities (“ARS”). Available-for-sale investments with contractual maturities of one year or less are classified as short-term in the Company's condensed consolidated balance sheets. Investments are carried at fair value.

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Policies)	9 Months Ended
	Sep. 30, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Currently, and from time to time, the Company is involved in litigation incidental to the conduct of its business. In accordance with GAAP, the Company records a provision for a liability when it is both probable that a liability has been incurred and the amount can be reasonably estimated.

SUMMARY OF SIGNIFICANT ACCOUN22

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	9 Months Ended
	Sep. 30, 2016
Accounting Policies [Abstract]
Schedule of accumulated other comprehensive loss	The components of accumulated other comprehensive loss were as follows (in thousands): September 30, December 31, Foreign currency translation adjustment $ (10,213 ) $ (7,159 ) Accumulated net unrealized loss on investments, net of tax (160 ) (435 ) Total accumulated other comprehensive loss $ (10,373 ) $ (7,594 )
Calculation of basic and diluted net income (loss) per share	The following table sets forth the calculation of basic and diluted net income (loss) per share (in thousands, except per share data): Three Months Ended Nine Months Ended Numerator: 2016 2015 2016 2015 Net income (loss) $ 23,201 $ (5,362 ) $ 55,498 $ (26,455 ) Denominator: Denominator for basic net income (loss) per share — weighted-average outstanding shares 32,186 31,980 32,152 31,934 Effect of dilutive securities: Stock options and restricted stock 254 — 271 — Denominator for diluted net income (loss) per share — weighted-average outstanding shares 32,440 31,980 32,423 31,934 Net income (loss) per share — basic $ 0.72 $ (0.17 ) $ 1.73 $ (0.83 ) Net income (loss) per share — diluted $ 0.72 $ (0.17 ) $ 1.71 $ (0.83 )
Schedule of anti-dilutive securities excluded from computation of earnings per share	The following table summarizes the shares underlying the performance-based restricted stock awards and service-based restricted stock units excluded from the basic and diluted calculation (in thousands): Three Months Ended Nine Months Ended 2016 2015 2016 2015 Performance-based restricted stock awards 72 55 72 55 Service-based restricted stock units 1 1 1 1 Total shares excluded from computation 73 56 73 56
Stock-based compensation expense for stock options and restricted stock	Stock-based compensation expense for stock options and restricted stock issued under equity incentive plans and stock purchases under the ESPP included in the Company’s results of operations were as follows (in thousands): Three Months Ended Nine Months Ended 2016 2015 2016 2015 Cost of revenues $ 1,396 $ 1,533 $ 4,209 $ 4,242 Selling and marketing 1,676 1,411 4,920 3,595 Software development 1,684 1,602 4,902 4,318 General and administrative 4,555 4,766 12,950 13,014 Total stock-based compensation $ 9,311 $ 9,312 $ 26,981 $ 25,169

ACQUISITION (Tables)

ACQUISITION (Tables)	9 Months Ended
	Sep. 30, 2016
Apartment Finder [Member]
Business Acquisition [Line Items]
Schedule of assets acquired and liabilities assumed	The following table summarizes the amounts for acquired assets and liabilities recorded at their fair values as of the acquisition date (in thousands): Cash and cash equivalents $ 39 Accounts receivable 4,556 Goodwill 107,692 Acquired trade names and other intangible assets 23,642 Acquired customer base 21,856 Acquired database technology 4,076 Acquired building photography 2,425 Deferred income taxes, net 9,290 Other assets and liabilities (849 ) Fair value of identifiable net assets acquired $ 172,727

INVESTMENTS (Tables)

INVESTMENTS (Tables)	9 Months Ended
	Sep. 30, 2016
Investments, Debt and Equity Securities [Abstract]
Scheduled maturities of investments classified as available-for-sale	Scheduled maturities of investments classified as available-for-sale as of September 30, 2016 are as follows (in thousands): Maturity Fair Value Due: October 1, 2016 — September 30, 2017 $ 1,171 October 1, 2017 — September 30, 2021 — October 1, 2021 — September 30, 2026 — After September 30, 2026 9,911 Available-for-sale investments $ 11,082
Schedule of available for sale securities reconciliation	As of September 30, 2016 , the amortized cost basis and fair value of investments classified as available-for-sale were as follows (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Auction rate securities $ 11,242 $ 728 $ (888 ) $ 11,082 Available-for-sale investments $ 11,242 $ 728 $ (888 ) $ 11,082 As of December 31, 2015 , the amortized cost basis and fair value of investments classified as available-for-sale were as follows (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Auction rate securities $ 15,942 $ 610 $ (1,045 ) $ 15,507 Available-for-sale investments $ 15,942 $ 610 $ (1,045 ) $ 15,507
Schedule of unrealized loss on investments for twelve months or longer	The components of the Company’s investments in an unrealized loss position for twelve months or longer were as follows (in thousands): September 30, December 31, Aggregate Fair Value Gross Unrealized Losses Aggregate Fair Value Gross Unrealized Losses Auction rate securities $ 9,911 $ (888 ) $ 14,455 $ (1,045 ) Investments in an unrealized loss position $ 9,911 $ (888 ) $ 14,455 $ (1,045 )

FAIR VALUE (Tables)

FAIR VALUE (Tables)	9 Months Ended
	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Summary of fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis	The following table represents the Company's fair value hierarchy for its financial assets (cash, cash equivalents and investments) measured at fair value on a recurring basis as of September 30, 2016 (in thousands): Level 1 Level 2 Level 3 Total Assets: Cash $ 338,510 $ — $ — $ 338,510 Money market funds 175,328 — — 175,328 Commercial paper 8,261 — — 8,261 Auction rate securities — — 11,082 11,082 Total assets measured at fair value $ 522,099 $ — $ 11,082 $ 533,181 The following table represents the Company's fair value hierarchy for its financial assets (cash, cash equivalents and investments) measured at fair value on a recurring basis as of December 31, 2015 (in thousands): Level 1 Level 2 Level 3 Total Assets: Cash $ 405,597 $ — $ — $ 405,597 Money market funds 5,043 — — 5,043 Commercial paper 11,178 — — 11,178 Auction rate securities — — 15,507 15,507 Total assets measured at fair value $ 421,818 $ — $ 15,507 $ 437,325
Summary of changes in the fair value of the company's level 3 assets	The following tables summarize changes in fair value of the Company’s Level 3 assets for the three and nine months ended September 30, 2016 and 2015 (in thousands): Three Months Ended Nine Months Ended 2016 2015 2016 2015 Balance at beginning of period $ 11,036 $ 16,049 $ 15,507 $ 17,151 Decrease in unrealized loss included in accumulated other comprehensive loss 46 8 275 256 Settlements — (550 ) (4,700 ) (1,900 ) Balance at end of period $ 11,082 $ 15,507 $ 11,082 $ 15,507 The following table summarizes changes in fair value of the Company’s Level 3 assets from December 31, 2014 to September 30, 2016 (in thousands): Auction Rate Securities Balance at December 31, 2014 $ 17,151 Decrease in unrealized loss included in accumulated other comprehensive loss 256 Settlements (1,900 ) Balance at December 31, 2015 15,507 Decrease in unrealized loss included in accumulated other comprehensive loss 275 Settlements (4,700 ) Balance at September 30, 2016 $ 11,082

GOODWILL (Tables)

GOODWILL (Tables)	9 Months Ended
	Sep. 30, 2016
Goodwill [Abstract]
Schedule of goodwill	The changes in the carrying amount of goodwill by operating segment consist of the following (in thousands): North America International Total Goodwill, December 31, 2014 $ 1,114,363 $ 24,442 $ 1,138,805 Acquisition 112,947 2,400 115,347 Effect of foreign currency translation — (1,207 ) (1,207 ) Goodwill, December 31, 2015 1,227,310 25,635 1,252,945 Acquisitions 467 5,933 6,400 Effect of foreign currency translation — (2,992 ) (2,992 ) Goodwill, September 30, 2016 $ 1,227,777 $ 28,576 $ 1,256,353

INTANGIBLE ASSETS (Tables)

INTANGIBLE ASSETS (Tables)	9 Months Ended
	Sep. 30, 2016
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Schedule of acquired finite-lived intangible assets by major class	Intangible assets consist of the following (in thousands, except amortization period data): September 30, December 31, Weighted- Average Amortization Period (in years) Capitalized product development cost $ 2,275 $ 2,243 4 Accumulated amortization (2,205 ) (2,172 ) Capitalized product development cost, net 70 71 Building photography 17,375 17,677 4 Accumulated amortization (16,246 ) (15,875 ) Building photography, net 1,129 1,802 Acquired database technology 78,332 77,905 5 Accumulated amortization (69,870 ) (62,818 ) Acquired database technology, net 8,462 15,087 Acquired customer base 221,385 221,409 10 Accumulated amortization (145,859 ) (129,782 ) Acquired customer base, net 75,526 91,627 Acquired trade names and other intangible assets 153,736 153,910 13 Accumulated amortization (31,810 ) (24,179 ) Acquired trade names and other intangible assets, net 121,926 129,731 Intangible assets, net $ 207,113 $ 238,318

LONG-TERM DEBT (Tables)

LONG-TERM DEBT (Tables)	9 Months Ended
	Sep. 30, 2016
Long-term Debt, Current and Noncurrent [Abstract]
Components of long-term debt	2015 . The following table represents the Company's long-term debt (in thousands): September 30, December 31, Term loan facility $ 345,000 $ 365,000 Debt issuance costs, net (7,481 ) (9,888 ) Total debt 337,519 355,112 Current maturities of long-term debt (25,000 ) (20,000 ) Current debt issuance costs, net 3,175 3,254 Total long-term debt, less current portion $ 315,694 $ 338,366

SEGMENT REPORTING (Tables)

SEGMENT REPORTING (Tables)	9 Months Ended
	Sep. 30, 2016
Segment Reporting [Abstract]
Summarized information by operating segment	Summarized information by operating segment consists of the following (in thousands): Three Months Ended Nine Months Ended 2016 2015 2016 2015 Revenues North America $ 205,637 $ 182,556 $ 598,757 $ 500,059 International External customers 7,074 6,522 20,562 18,696 Intersegment revenue 3 4 24 25 Total International revenue 7,077 6,526 20,586 18,721 Intersegment eliminations (3 ) (4 ) (24 ) (25 ) Total revenues $ 212,711 $ 189,078 $ 619,319 $ 518,755 EBITDA North America $ 56,305 $ 20,993 $ 148,296 $ 32,816 International 1,371 1,096 2,761 2,124 Total EBITDA $ 57,676 $ 22,089 $ 151,057 $ 34,940
Reconciliation of net income (loss) to EBITDA	The reconciliation of net income (loss) to EBITDA consists of the following (in thousands): Three Months Ended Nine Months Ended 2016 2015 2016 2015 Net income (loss) $ 23,201 $ (5,362 ) $ 55,498 $ (26,455 ) Purchase amortization in cost of revenues 5,736 9,964 17,119 22,887 Purchase amortization in operating expenses 5,550 7,153 17,602 21,260 Depreciation and other amortization 6,794 5,403 18,320 14,860 Interest income (344 ) (42 ) (587 ) (473 ) Interest expense 2,498 2,363 7,462 7,060 Income tax expense (benefit), net 14,241 2,610 35,643 (4,199 ) EBITDA $ 57,676 $ 22,089 $ 151,057 $ 34,940
Summarized information by operating segment, assets and liabilities	Summarized information by operating segment consists of the following (in thousands): September 30, December 31, Property and equipment, net North America $ 83,415 $ 86,191 International 1,951 2,120 Total property and equipment, net $ 85,366 $ 88,311 Goodwill North America $ 1,227,777 $ 1,227,310 International 28,576 25,635 Total goodwill $ 1,256,353 $ 1,252,945 Assets North America $ 2,205,725 $ 2,130,202 International 45,990 41,370 Total operating segment assets $ 2,251,715 $ 2,171,572 Reconciliation of operating segment assets to total assets Total operating segment assets $ 2,251,715 $ 2,171,572 Investment in subsidiaries (18,344 ) (18,344 ) Intersegment receivables (80,784 ) (73,657 ) Total assets $ 2,152,587 $ 2,079,571 Liabilities North America $ 523,844 $ 525,566 International 71,094 72,544 Total operating segment liabilities $ 594,938 $ 598,110 Reconciliation of operating segment liabilities to total liabilities Total operating segment liabilities $ 594,938 $ 598,110 Intersegment payables (61,049 ) (62,319 ) Total liabilities $ 533,889 $ 535,791
Revenues by services	The revenue by type of service consists of the following (in thousands): Three Months Ended Nine Months Ended 2016 2015 2016 2015 Information and analytics CoStar Suite (1) $ 103,261 $ 91,350 $ 301,969 $ 266,931 Information services (2) 19,486 19,126 58,336 56,415 Online marketplaces Multifamily (3) 57,654 49,312 164,752 110,187 Commercial property and land (4) 32,310 29,290 94,262 85,222 Total revenues $ 212,711 $ 189,078 $ 619,319 $ 518,755 (1) CoStar Suite is comprised of CoStar Property Professional, CoStar COMPS Professional, CoStar Tenant; CoStar Market Analytics; and CoStar Portfolio Strategy. (2) Information services is comprised of LoopNet Premium Searcher; CoStar Real Estate Manager; CoStar Risk Analytics COMPASS; CoStar Investment Analysis Portfolio Maximizer; CoStar Investment Analysis Request; CoStar Brokerage Applications; PROPEX; Grecam; Belbex and Thomas Daily. (3) Multifamily is comprised of Apartments.com, ApartmentFinder.com and ApartmentHomeLiving.com. (4) Commercial property and land is comprised of LoopNet Premium Lister; LoopLink; CoStar Advertising; BizBuySell and BizQuest; LandsofAmerica and LandAndFarm; and CoStar Private Sale Network.

ORGANIZATION (Details)

ORGANIZATION (Details)	9 Months Ended
	Sep. 30, 2016operating_segments
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of business segments (in segments)	2
Term of subscription-based license agreements (in years)	1 year

SUMMARY OF SIGNIFICANT ACCOUN31

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, ADVERTISING COSTS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accounting Policies [Abstract]
Advertising expense	$ 27	$ 34	$ 95	$ 113

SUMMARY OF SIGNIFICANT ACCOUN32

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, FOREIGN CURRENCY AND ACCUMULATED OTHER COMPREHENSIVE LOSS, NET OF TAX (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Accounting Policies [Abstract]
Material gains or losses from foreign currency transactions	$ 0	$ 0	$ 0	$ 0
Accumulated Other Comprehensive Loss Net of Tax [Abstract]
Foreign currency translation adjustment	(10,213,000)		(10,213,000)		$ (7,159,000)
Accumulated net unrealized loss on investments, net of tax	(160,000)		(160,000)		(435,000)
Total accumulated other comprehensive loss	(10,373,000)		(10,373,000)		$ (7,594,000)
Reclassification out of accumulated other comprehensive loss	$ 0	$ 0	$ 0	$ 0

SUMMARY OF SIGNIFICANT ACCOUN33

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, NET INCOME (LOSS) PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	73	56	73	56
Numerator: [Abstract]
Net income (loss)	$ 23,201	$ (5,362)	$ 55,498	$ (26,455)
Denominator: [Abstract]
Denominator for basic net income (loss) per share - weighted-average outstanding shares (in shares)	32,186	31,980	32,152	31,934
Effect of dilutive securities: [Abstract]
Stock options and restricted stock	254	0	271	0
Denominator for diluted net income (loss) per share - weighted-average outstanding shares (in shares)	32,440	31,980	32,423	31,934
Net income (loss) per share - basic (in dollars per share)	$ 0.72	$ (0.17)	$ 1.73	$ (0.83)
Net income (loss) per share - diluted (in dollars per share)	$ 0.72	$ (0.17)	$ 1.71	$ (0.83)
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	89		184
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	72	55	72	55
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	1	1	1	1

SUMMARY OF SIGNIFICANT ACCOUN34

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, STOCK BASED COMPENSATION EXPENSE (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Stock-Based Compensation Expense [Abstract]
Net cash proceeds from the exercise of stock options and Employee Stock Purchase Plan	$ 1,000	$ 646	$ 4,791	$ 5,350
Excess tax benefits realized from stock option exercised and restricted stock awards vested	398	418	5,000	8,000
Compensation expense	$ 9,311	$ 9,312	$ 26,981	$ 25,169
Exercise of stock options (in shares)	3,367	0	24,078	41,068
Cost of Revenues [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	$ 1,396	$ 1,533	$ 4,209	$ 4,242
Selling and Marketing [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	1,676	1,411	4,920	3,595
Software Development [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	1,684	1,602	4,902	4,318
General and Administrative [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	$ 4,555	$ 4,766	$ 12,950	$ 13,014

SUMMARY OF SIGNIFICANT ACCOUN35

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, DEBT ISSUANCE COSTS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Deferred Finance Costs, Own-share Lending Arrangement, Issuance Costs, Net [Abstract]
Capitalized debt issuance costs	$ 7,481		$ 7,481		$ 9,888
Amortization of debt issuance costs	$ 797	$ 830	$ 2,000	$ 2,000

ACQUISITION, APARTMENT FINDER (

ACQUISITION, APARTMENT FINDER (Details)	Jun. 01, 2015USD ($)distinct_intangible_asset	Sep. 30, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Business Acquisition [Line Items]
Goodwill		$ 1,256,353,000	$ 1,252,945,000	$ 1,138,805,000
Apartment Finder [Member]
Business Acquisition [Line Items]
Percentage of outstanding stock acquired by the Company	100.00%
Payments to acquire businesses	$ 173,000,000
Closing purchase price adjustments	3,000,000
Post closing purchase price adjustments	21,000
Goodwill	107,692,000
Goodwill tax deductible amount	$ 0
Trade Names and Other Intangible Assets [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets		13 years
Trade Names and Other Intangible Assets [Member] | Apartment Finder [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets	9 years
Customer Contracts [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets		10 years
Customer Contracts [Member] | Apartment Finder [Member]
Business Acquisition [Line Items]
Number of distinct intangible assets | distinct_intangible_asset	3
Estimated useful life of acquired assets	10 years
Developed Technology Rights [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets		5 years
Developed Technology Rights [Member] | Apartment Finder [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets	5 months
Building Photography [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets		4 years
Building Photography [Member] | Apartment Finder [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets	5 months

ACQUISITION, SCHEDULE OF ASSETS

ACQUISITION, SCHEDULE OF ASSETS ACQUIRED AND LIABILITIES ASSUMED FOR APARTMENT FINDER (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Jun. 01, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill	$ 1,256,353	$ 1,252,945		$ 1,138,805
Apartment Finder [Member]
Business Acquisition [Line Items]
Cash and cash equivalents			$ 39
Accounts receivable			4,556
Goodwill			107,692
Deferred income taxes, net			9,290
Other assets and liabilities			(849)
Fair value of identifiable net assets acquired			172,727
Trade Names and Other Intangible Assets [Member] | Apartment Finder [Member]
Business Acquisition [Line Items]
Intangible assets, other than goodwill			23,642
Customer Contracts [Member] | Apartment Finder [Member]
Business Acquisition [Line Items]
Intangible assets, other than goodwill			21,856
Developed Technology Rights [Member] | Apartment Finder [Member]
Business Acquisition [Line Items]
Intangible assets, other than goodwill			4,076
Building Photography [Member] | Apartment Finder [Member]
Business Acquisition [Line Items]
Intangible assets, other than goodwill			$ 2,425

INVESTMENTS, SCHEDULED MATURITI

INVESTMENTS, SCHEDULED MATURITIES AND REALIZED GAINS AND LOSSES (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Debt Maturities Fair Value [Abstract]
October 1, 2016 — September 30, 2017	$ 1,171,000		$ 1,171,000
October 1, 2017 — September 30, 2021	0		0
October 1, 2021 — September 30, 2026	0		0
After September 30, 2026	9,911,000		9,911,000
Available-for-sale investments	11,082,000		11,082,000		$ 15,507,000
Available-for-sale securities, gross realized gains	0	$ 0	0	$ 0
Available-for-sale securities, gross realized losses	$ 0	$ 0	$ 0	$ 0

INVESTMENTS, AVAILABLE-FOR-SALE

INVESTMENTS, AVAILABLE-FOR-SALE SECURITIES (Details) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Available-for-sale Securities Reconciliation [Abstract]
Amortized cost	$ 11,242,000	$ 15,942,000
Gross unrealized gains	728,000	610,000
Gross unrealized losses	(888,000)	(1,045,000)
Fair value	11,082,000	15,507,000
Available-For-Sale Securities, Unrealized Loss Positions [Abstract]
Continuous unrealized loss position, 12 months or more, aggregated fair value	9,911,000	14,455,000
Continuous unrealized loss position, 12 months or more, gross unrealized losses	(888,000)	(1,045,000)
Continuous unrealized loss position, less than 12 months, accumulated loss	0	0
Auction Rate Securities [Member]
Available-for-sale Securities Reconciliation [Abstract]
Amortized cost	11,242,000	15,942,000
Gross unrealized gains	728,000	610,000
Gross unrealized losses	(888,000)	(1,045,000)
Fair value	11,082,000	15,507,000
Available-For-Sale Securities, Unrealized Loss Positions [Abstract]
Continuous unrealized loss position, 12 months or more, aggregated fair value	9,911,000	14,455,000
Continuous unrealized loss position, 12 months or more, gross unrealized losses	$ (888,000)	$ (1,045,000)

FAIR VALUE (Details)

FAIR VALUE (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Unobservable inputs assets (level 3) [Roll forward]
Beginning balance	$ 11,036	$ 16,049	$ 15,507	$ 17,151	$ 17,151
Change in unrealized gain (loss) included in accumulated other comprehensive loss	46	8	275	256
Settlements	0	(550)	(4,700)	(1,900)
Ending balance	11,082	$ 15,507	11,082	15,507	15,507
Temporary impairment of the auction rates security investments, net of unrealized gain	(160)		(160)		(435)
Fair Value, Measurements, Recurring [Member]
Assets:
Total assets measured at fair value	533,181		533,181		437,325
Fair Value, Measurements, Recurring [Member] | Cash [Member]
Assets:
Total assets measured at fair value	338,510		338,510		405,597
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Assets:
Total assets measured at fair value	175,328		175,328		5,043
Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member]
Assets:
Total assets measured at fair value	8,261		8,261		11,178
Fair Value, Measurements, Recurring [Member] | Auction Rate Securities [Member]
Assets:
Total assets measured at fair value	11,082		11,082		15,507
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets:
Total assets measured at fair value	522,099		522,099		421,818
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Cash [Member]
Assets:
Total assets measured at fair value	338,510		338,510		405,597
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Assets:
Total assets measured at fair value	175,328		175,328		5,043
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commercial Paper [Member]
Assets:
Total assets measured at fair value	8,261		8,261		11,178
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Auction Rate Securities [Member]
Assets:
Total assets measured at fair value	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets:
Total assets measured at fair value	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Cash [Member]
Assets:
Total assets measured at fair value	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Assets:
Total assets measured at fair value	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial Paper [Member]
Assets:
Total assets measured at fair value	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Auction Rate Securities [Member]
Assets:
Total assets measured at fair value	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets:
Total assets measured at fair value	11,082		11,082		15,507
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Cash [Member]
Assets:
Total assets measured at fair value	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member]
Assets:
Total assets measured at fair value	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commercial Paper [Member]
Assets:
Total assets measured at fair value	0		0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Auction Rate Securities [Member]
Assets:
Total assets measured at fair value	11,082		11,082		15,507
Auction Rate Securities [Member]
Unobservable inputs assets (level 3) [Roll forward]
Beginning balance			15,507	$ 17,151	17,151
Change in unrealized gain (loss) included in accumulated other comprehensive loss			275		256
Settlements			(4,700)		(1,900)
Ending balance	11,082		$ 11,082		$ 15,507
Auction rate securities variable rate debt instruments interest rate reset period			28 days
The minimum contractual maturities on underlying securities involved in auction rate securities			20 years
Par value of company held auction rate securities	12,000		$ 12,000
Discount rate (in percent)			6.00%		5.00%
Temporary impairment of the auction rates security investments, net of unrealized gain	$ (160)		$ (160)

GOODWILL (Details)

GOODWILL (Details) - USD ($) $ in Thousands	May 03, 2016	Jul. 01, 2015	Jun. 01, 2015	Sep. 30, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Goodwill, beginning balance				$ 1,252,945	$ 1,138,805
Acquisition				6,400	115,347
Effect of foreign currency translation				(2,992)	(1,207)
Goodwill, ending balance				1,256,353	1,252,945
Apartment Finder [Member]
Goodwill [Roll Forward]
Acquisition			$ 108,000
Goodwill, ending balance			$ 107,692
Belbex [Member]
Goodwill [Roll Forward]
Acquisition		$ 2,000
Independent Distributor Buyout [Member]
Goodwill [Roll Forward]
Acquisition				467	5,000
Thomas Daily [Member]
Goodwill [Roll Forward]
Acquisition	$ 6,000
North America [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance				1,227,310	1,114,363
Acquisition				467	112,947
Effect of foreign currency translation				0	0
Goodwill, ending balance				1,227,777	1,227,310
International [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance				25,635	24,442
Acquisition				5,933	2,400
Effect of foreign currency translation				(2,992)	(1,207)
Goodwill, ending balance				$ 28,576	$ 25,635

INTANGIBLE ASSETS (Details)

INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands	Jun. 01, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net		$ 207,113		$ 238,318
Impairment of intangible assets, finite-lived		0	$ 2,778
Capitalized Product Development Costs [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross		2,275		2,243
Finite-lived intangible assets, accumulated amortization		(2,205)		(2,172)
Finite-lived intangible assets, net		$ 70		71
Weighted-average amortization period (in years}		4 years
Building Photography [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross		$ 17,375		17,677
Finite-lived intangible assets, accumulated amortization		(16,246)		(15,875)
Finite-lived intangible assets, net		$ 1,129		1,802
Weighted-average amortization period (in years}		4 years
Developed Technology Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross		$ 78,332		77,905
Finite-lived intangible assets, accumulated amortization		(69,870)		(62,818)
Finite-lived intangible assets, net		$ 8,462		15,087
Weighted-average amortization period (in years}		5 years
Acquired Customer Base [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross		$ 221,385		221,409
Finite-lived intangible assets, accumulated amortization		(145,859)		(129,782)
Finite-lived intangible assets, net		$ 75,526		91,627
Weighted-average amortization period (in years}		10 years
Trade Names and Other Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross		$ 153,736		153,910
Finite-lived intangible assets, accumulated amortization		(31,810)		(24,179)
Finite-lived intangible assets, net		$ 121,926		$ 129,731
Weighted-average amortization period (in years}		13 years
Apartments.com [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Impairment of intangible assets, finite-lived			1,000
Apartment Finder [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Impairment of intangible assets, finite-lived			$ 1,000
Apartment Finder [Member] | Building Photography [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}	5 months
Apartment Finder [Member] | Developed Technology Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}	5 months
Apartment Finder [Member] | Acquired Customer Base [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}	10 years
Apartment Finder [Member] | Trade Names and Other Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}	9 years
LoopNet [Member] | Trade Names and Other Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}		15 years

LONG-TERM DEBT (Details)

LONG-TERM DEBT (Details) - USD ($)	Apr. 02, 2014	Jun. 30, 2014	Sep. 30, 2016	Dec. 31, 2015	Apr. 01, 2014
Debt Instrument [Line Items]
Line of credit facility, amount outstanding					$ 150,000,000
Repayments of revolving credit facility		$ 150,000,000
Repayments of term loan	$ 149,000,000
LIBOR maturity period (in months)	1 month
Default interest rate per annum on overdue amounts (in percent)					2.00%
Credit facility, collateral			The obligations under the 2014 Credit Agreement are guaranteed by all material subsidiaries of the Company and are secured by a lien on substantially all of the assets of the Company and those of its material subsidiaries, in each case subject to certain exceptions, pursuant to security and guarantee documents entered into on the Closing Date.
Capitalized debt issuance costs					$ 10,000,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, amount outstanding			$ 0	$ 0
CoStar Group [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Debt instrument borrowing capacity					400,000,000
Term of loan (in years)	5 years
CoStar Group [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument borrowing capacity					225,000,000
Term of loan (in years)	5 years
CoStar Group [Member] | Swingline Loan [Member]
Debt Instrument [Line Items]
Revolving credit sub-facility for swing-line loans and issuances of letters of credit					10,000,000
CoStar Group [Member] | Letter of Credit [Member]
Debt Instrument [Line Items]
Revolving credit sub-facility for swing-line loans and issuances of letters of credit					$ 10,000,000
CoStar Group [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Annual amortization, first year after closing (in percent)					5.00%
Annual amortization, second year after closing (in percent)					5.00%
Annual amortization, third year after closing (in percent)					5.00%
Annual amortization, fourth year after closing (in percent)					10.00%
Annual amortization, fifth year after closing (in percent)					15.00%
Federal Funds Rate [Member]
Debt Instrument [Line Items]
Basis spread on federal funds rate (in percent)	0.50%
LIBOR [Member]
Debt Instrument [Line Items]
Basis spread on federal funds rate (in percent)	2.00%
Debt instrument, basis spread on variable rate, one month interest period (in percent)					1.00%
Debt instrument, basis spread on variable rate, per annum (in percent)					1.00%

LONG-TERM DEBT, COVENANT CALCUL

LONG-TERM DEBT, COVENANT CALCULATIONS (Details)	Apr. 01, 2014
Debt Disclosure [Abstract]
Maximum first lien secured leverage ratio after eight fiscal quarters after closing date (in percent)	350.00%
Maximum total leverage ratio after eight fiscal quarters after closing date (in percent)	450.00%

LONG-TERM DEBT, INTEREST EXPENS

LONG-TERM DEBT, INTEREST EXPENSE AND AMORTIZATION OF DEBT ISSUANCE COSTS (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Apr. 01, 2014
Debt Instrument [Line Items]
Line of credit facility, amount outstanding						$ 150,000,000
Interest expense, debt	$ 2,000,000	$ 2,000,000	$ 7,000,000	$ 7,000,000
Amortization of debt issuance costs	797,000	830,000	2,000,000	2,000,000
Interest paid	2,000,000	$ 2,000,000	5,000,000	$ 5,000,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, amount outstanding	$ 0		$ 0		$ 0

LONG-TERM DEBT, COMPONENTS OF L

LONG-TERM DEBT, COMPONENTS OF LONG-TERM DEBT (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Term loan facility	$ 345,000	$ 365,000
Debt issuance costs, net	(7,481)	(9,888)
Total debt	337,519	355,112
Current maturities of long-term debt	(25,000)	(20,000)
Current debt issuance costs, net	3,175	3,254
Total long-term debt, less current portion	$ 315,694	$ 338,366

INCOME TAXES (Details)

INCOME TAXES (Details)	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Effective income tax rate (in percent)	39.00%	14.00%

COMMITMENTS AND CONTINGENCIES48

COMMITMENTS AND CONTINGENCIES (Details) - CoStar Group [Member] - USD ($)	Apr. 02, 2014	Apr. 01, 2014
Term Loan [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity		$ 400,000,000
Term of loan (in years)	5 years
Revolving Credit Facility [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity		$ 225,000,000
Term of loan (in years)	5 years

SEGMENT REPORTING (Details)

SEGMENT REPORTING (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016USD ($)	Sep. 30, 2015USD ($)	Sep. 30, 2016USD ($)operating_segments	Sep. 30, 2015USD ($)
Segment Reporting Information [Line Items]
Number of business segments (in segments) | operating_segments			2
Segment Reporting Information, Revenue [Abstract]
Revenues	$ 212,711	$ 189,078	$ 619,319	$ 518,755
Reconciliation of EBITDA to net income (loss) [Abstract]
Net income (loss)	23,201	(5,362)	55,498	(26,455)
Purchase amortization in cost of revenues	5,736	9,964	17,119	22,887
Purchase amortization in operating expenses	5,550	7,153	17,602	21,260
Depreciation and other amortization	6,794	5,403	18,320	14,860
Interest income	(344)	(42)	(587)	(473)
Interest expense	2,498	2,363	7,462	7,060
Income tax expense (benefit), net	14,241	2,610	35,643	(4,199)
EBITDA	57,676	22,089	151,057	34,940
Intersegment Revenue [Member]
Segment Reporting Information, Revenue [Abstract]
Revenues	3	4	24	25
Operating Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
North America corporate allocation	70	225	379	763
Segment Reporting Information, Revenue [Abstract]
Revenues	205,637	182,556	598,757	500,059
Reconciliation of EBITDA to net income (loss) [Abstract]
EBITDA	56,305	20,993	148,296	32,816
Operating Segments [Member] | International [Member]
Segment Reporting Information [Line Items]
International corporate allocation	113	74	246	200
Segment Reporting Information, Revenue [Abstract]
Revenues	7,077	6,526	20,586	18,721
Reconciliation of EBITDA to net income (loss) [Abstract]
EBITDA	1,371	1,096	2,761	2,124
Operating Segments [Member] | International [Member] | External Customers [Member]
Segment Reporting Information, Revenue [Abstract]
Revenues	7,074	6,522	20,562	18,696
Intersegment Eliminations [Member]
Segment Reporting Information, Revenue [Abstract]
Revenues	$ (3)	$ (4)	$ (24)	$ (25)

SEGMENT REPORTING, ASSETS AND L

SEGMENT REPORTING, ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Property and equipment, net	$ 85,366	$ 88,311
Goodwill	1,256,353	1,252,945	$ 1,138,805
Reconciliation of operating segment assets to total assets [Abstract]
Total assets	2,152,587	2,079,571
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total liabilities	533,889	535,791
North America [Member]
Segment Reporting Information [Line Items]
Goodwill	1,227,777	1,227,310	1,114,363
International [Member]
Segment Reporting Information [Line Items]
Goodwill	28,576	25,635	$ 24,442
Operating Segments [Member]
Reconciliation of operating segment assets to total assets [Abstract]
Total assets	2,251,715	2,171,572
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total liabilities	594,938	598,110
Operating Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
Property and equipment, net	83,415	86,191
Goodwill	1,227,777	1,227,310
Reconciliation of operating segment assets to total assets [Abstract]
Total assets	2,205,725	2,130,202
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total liabilities	523,844	525,566
Operating Segments [Member] | International [Member]
Segment Reporting Information [Line Items]
Property and equipment, net	1,951	2,120
Goodwill	28,576	25,635
Reconciliation of operating segment assets to total assets [Abstract]
Total assets	45,990	41,370
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total liabilities	71,094	72,544
Consolidation, Eliminations [Member]
Reconciliation of operating segment assets to total assets [Abstract]
Total assets	(18,344)	(18,344)
Intersegment Eliminations [Member]
Reconciliation of operating segment assets to total assets [Abstract]
Total assets	(80,784)	(73,657)
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total liabilities	$ (61,049)	$ (62,319)

SEGMENT REPORTING, REVENUES BY

SEGMENT REPORTING, REVENUES BY SERVICES (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Revenue from External Customer [Line Items]
Revenues		$ 212,711	$ 189,078	$ 619,319	$ 518,755
CoStar Suite [Member]
Revenue from External Customer [Line Items]
Revenues	[1]	103,261	91,350	301,969	266,931
Information services [Member]
Revenue from External Customer [Line Items]
Revenues	[2]	19,486	19,126	58,336	56,415
Multifamily [Member]
Revenue from External Customer [Line Items]
Revenues	[3]	57,654	49,312	164,752	110,187
Commercial property and land [Member]
Revenue from External Customer [Line Items]
Revenues	[4]	$ 32,310	$ 29,290	$ 94,262	$ 85,222
[1]	CoStar Suite is comprised of CoStar Property Professional, CoStar COMPS Professional, CoStar Tenant; CoStar Market Analytics; and CoStar Portfolio Strategy.
[2]	Information services is comprised of LoopNet Premium Searcher; CoStar Real Estate Manager; CoStar Risk Analytics COMPASS; CoStar Investment Analysis Portfolio Maximizer; CoStar Investment Analysis Request; CoStar Brokerage Applications; PROPEX; Grecam; Belbex and Thomas Daily.
[3]	Multifamily is comprised of Apartments.com, ApartmentFinder.com and ApartmentHomeLiving.com.
[4]	Commercial property and land is comprised of LoopNet Premium Lister; LoopLink; CoStar Advertising; BizBuySell and BizQuest; LandsofAmerica and LandAndFarm; and CoStar Private Sale Network.