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Document And Entity Information - shares	9 Months Ended
Document And Entity Information - shares	Sep. 30, 2015	Oct. 23, 2015
Document and Entity Information [Abstract]
Entity Registrant Name	COSTAR GROUP INC
Entity Central Index Key	0001057352
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		32,488,830

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement [Abstract]
Revenues	$ 189,078	$ 153,056	$ 518,755	$ 419,840
Cost of revenues	53,728	40,932	143,758	114,056
Gross margin	135,350	112,124	374,997	305,784
Operating expenses:
Selling and marketing	80,506	40,668	242,418	109,302
Software development	17,048	14,227	49,040	41,721
General and administrative	31,074	25,388	86,346	76,535
Purchase amortization	7,153	8,361	21,260	20,696
Total operating expenses	135,781	88,644	399,064	248,254
Income (loss) from operations	(431)	23,480	(24,067)	57,530
Interest and other income	42	46	473	245
Interest and other expense	(2,363)	(2,698)	(7,060)	(8,066)
Income (loss) before income taxes	(2,752)	20,828	(30,654)	49,709
Income tax expense (benefit), net	2,610	7,871	(4,199)	18,763
Net income (loss)	$ (5,362)	$ 12,957	$ (26,455)	$ 30,946
Net income (loss) per share-basic (in dollars per share)	$ (0.17)	$ 0.41	$ (0.83)	$ 1.04
Net income (loss) per share-diluted (in dollars per share)	$ (0.17)	$ 0.40	$ (0.83)	$ 1.03
Weighted average outstanding shares-basic (in shares)	31,980	31,742	31,934	29,692
Weighted average outstanding shares-diluted (in shares)	31,980	32,075	31,934	30,134

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (5,362)	$ 12,957	$ (26,455)	$ 30,946
Other comprehensive loss, net of tax
Foreign currency translation adjustment	(965)	(1,413)	(719)	(452)
Net decrease in unrealized loss on investments	8	42	256	241
Total other comprehensive loss	(957)	(1,371)	(463)	(211)
Total comprehensive income (loss)	$ (6,319)	$ 11,586	$ (26,918)	$ 30,735

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 375,509	$ 527,012
Accounts receivable, net of allowance for doubtful accounts of approximately $7,627 and $4,815 as of September 30, 2015 and December 31, 2014, respectively	51,066	38,694
Deferred and other income taxes, net	35,246	20,007
Income tax receivable	1,027	1,027
Prepaid expenses and other current assets	10,350	9,736
Debt issuance costs, net	3,276	3,335
Total current assets	476,474	599,811
Long-term investments	15,507	17,151
Property and equipment, net	87,627	73,753
Goodwill	1,249,945	1,138,805
Intangible assets, net	250,813	241,622
Deposits and other assets	2,933	2,676
Debt issuance costs, net	7,437	9,864
Total assets	2,090,736	2,083,682
Current liabilities:
Current portion of long-term debt	20,000	20,000
Accounts payable	14,210	8,608
Accrued wages and commissions	30,197	23,155
Accrued expenses	39,272	27,001
Deferred gain on the sale of building	2,523	2,523
Income taxes payable	11,702	0
Deferred rent	1,104	0
Deferred revenue	43,910	38,003
Total current liabilities	162,918	119,290
Long-term debt, less current portion	350,000	365,000
Deferred gain on the sale of building	21,870	23,762
Deferred rent	29,927	27,032
Deferred income taxes, net	11,262	30,349
Income taxes payable	4,801	4,703
Total liabilities	580,778	570,136
Stockholders' equity:
Total stockholders’ equity	1,509,958	1,513,546
Total liabilities and stockholders’ equity	$ 2,090,736	$ 2,083,682

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Current assets:
Allowance for doubtful accounts	$ 7,627	$ 4,815

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Operating activities:
Net income (loss)	$ (26,455)	$ 30,946
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation	14,445	11,089
Amortization	44,562	39,644
Amortization of debt issuance costs	2,486	2,459
Impairment loss	2,778	1,799
Excess tax benefit from stock-based compensation	(7,970)	(28,167)
Stock-based compensation expense	25,169	20,906
Deferred income tax benefit, net	(13,702)	(1,236)
Provision for losses on accounts receivable	5,490	3,798
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable	(13,279)	(11,575)
Prepaid expenses and other current assets	263	(2,306)
Deposits and other assets	411	(68)
Accounts payable and other liabilities	30,085	24,712
Deferred revenue	5,433	4,035
Net cash provided by operating activities	69,716	96,036
Investing activities:
Proceeds from sale and settlement of investments	1,900	1,150
Purchases of property and equipment and other assets	(27,953)	(20,865)
Acquisitions, net of cash acquired	(177,476)	(584,218)
Net cash used in investing activities	(203,529)	(603,933)
Financing activities:
Proceeds from long-term debt	0	550,000
Payments of long-term debt	(15,000)	(313,125)
Payments of debt issuance costs	0	(9,969)
Payments of deferred consideration	0	(1,344)
Excess tax benefit from stock-based compensation	7,970	28,167
Repurchase of restricted stock to satisfy tax withholding obligations	(15,816)	(49,998)
Proceeds from equity offering, net of transaction costs	0	529,360
Proceeds from exercise of stock options and employee stock purchase plan	5,350	5,157
Net cash provided by (used in) financing activities	(17,496)	738,248
Effect of foreign currency exchange rates on cash and cash equivalents	(194)	(109)
Net increase (decrease) in cash and cash equivalents	(151,503)	230,242
Cash and cash equivalents at the beginning of period	527,012	255,953
Cash and cash equivalents at the end of period	$ 375,509	$ 486,195

ORGANIZATION	9 Months Ended
ORGANIZATION	Sep. 30, 2015
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.”), parts of Canada, Madrid, Spain and parts of 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 ACCOUNTING POLICIES

9 Months Ended

Sep. 30, 2015

Accounting Policies [Abstract]

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, 2015 and December 31, 2014, the results of its operations for the three and nine months ended September 30, 2015 and 2014, its comprehensive income (loss) for the three and nine months ended September 30, 2015 and 2014, and its cash flows for the nine months ended September 30, 2015 and 2014. 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, 2014.

The results of operations for the three and nine months ended September 30, 2015 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, 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.

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 $33.5 million and $8.7 million for the three months ended September 30, 2015 and 2014, respectively. Advertising costs were approximately $112.5 million and $20.2 million for the nine months ended September 30, 2015 and 2014, respectively.


2.	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED)

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, 2015 and 2014.

Accumulated Other Comprehensive Loss

The components of accumulated other comprehensive loss were as follows (in thousands):



	September 30, 2015			December 31, 2014
Foreign currency translation adjustment	$	(6,412	)	$	(5,693	)
Accumulated net unrealized loss on investments, net of tax	(435		)	(691		)
Total accumulated other comprehensive loss	$	(6,847	)	$	(6,384	)

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, 2015 and 2014.

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.

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 September 30,					Nine Months Ended September 30,
Numerator:	2015			2014		2015			2014
Numerator:
Net income (loss)	$	(5,362	)	$	12,957	$	(26,455	)	$	30,946
Denominator:
Denominator for basic net income (loss) per share — weighted-average outstanding shares	31,980			31,742		31,934			29,692
Effect of dilutive securities:
Stock options and restricted stock	—			333		—			442
Denominator for diluted net income (loss) per share — weighted-average outstanding shares	31,980			32,075		31,934			30,134

Net income (loss) per share — basic	$	(0.17	)	$	0.41	$	(0.83	)	$	1.04
Net income (loss) per share — diluted	$	(0.17	)	$	0.40	$	(0.83	)	$	1.03


2.	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED)

Net Income (Loss) Per Share — (Continued)

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. Stock options to purchase approximately 80,000 shares that were outstanding for the three and nine months ended September 30, 2014 were not included in the computation of diluted net income per share because the exercise price of the stock options was greater than the average market share price of the common stock during the period. Additionally, shares underlying restricted common stock awards and restricted stock units that vest based on Company performance and/or 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 September 30,		Nine Months Ended September 30,
	2015	2014	2015	2014
Performance-based restricted stock awards	55	23	55	23
Service-based restricted stock units	1	1	1	1
Total shares excluded from computation	56	24	56	24

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.

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 $646,000 and $1.6 million for the three months ended September 30, 2015 and 2014, respectively. Net cash proceeds from the exercise of stock options and the purchase of shares under the ESPP were approximately $5.4 million and $5.2 million for the nine months ended September 30, 2015 and 2014, respectively. The Company realized approximately $418,000 and $1.3 million of excess tax benefits from stock options exercised and restricted stock awards vested for the three months ended September 30, 2015 and September 30, 2014, respectively. The Company realized approximately $8.0 million and $28.2 million of excess tax benefits from stock options exercised and restricted stock awards vested for the nine months ended September 30, 2015 and 2014, respectively.


2.	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED)

Stock-Based Compensation — (Continued)

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 September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014
Cost of revenues	$	1,533	$	1,067	$	4,242	$	3,331
Selling and marketing	1,411		954		3,595		2,729
Software development	1,602		1,179		4,318		3,867
General and administrative	4,766		3,447		13,014		10,979
Total stock-based compensation	$	9,312	$	6,647	$	25,169	$	20,906

There were no options exercised during the three months ended September 30, 2015. Options to purchase 20,366 shares were exercised during the three months ended September 30, 2014. Options to purchase 41,068 and 66,201 shares were exercised during the nine months ended September 30, 2015 and 2014, respectively.

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. 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 of approximately $10.7 million and $13.2 million as of September 30, 2015 and December 31, 2014, 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 $830,000 and $904,000 for the three months ended September 30, 2015 and 2014, respectively. The Company amortized debt issuance costs of approximately $2.5 million for each of the nine months ended September 30, 2015 and 2014.

Business Combinations

The Company allocates the fair value of 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. Upon the conclusion of the measurement period, any subsequent adjustments are recorded to earnings. See Note 3 for additional information regarding the Company's recent business combinations.


2.	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED)

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, 2014, including the expected dates of adoption and estimated effects on the Company’s condensed consolidated financial statements, except for the following:

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 U.S. GAAP and International Financial Reporting Standards (“IFRS”). This guidance provides a more robust framework for addressing revenue issues, improves the comparability of revenue recognition practices across industries, provides more 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 goods 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. 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. The original effective date of the new standard was for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. In August 2015, the FASB issued an accounting standards update that defers by one year the effective date of this new revenue recognition standard. As a result, the new standard will be effective for annual reporting periods beginning after December 15, 2017, with an option that permits companies to adopt the standard as early as the original effective date. Early application prior to the original effective date is not permitted. The Company has not yet determined when it will adopt the standard and it has not selected a transition method and is currently evaluating the impact this guidance will have on its financial statements.

In April 2015, the FASB issued authoritative guidance to simplify the presentation of debt issuance costs. This guidance requires a company to present debt issuance costs related to a recognized debt liability in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by this guidance. In August 2015, the FASB issued an accounting standards update to address the presentation and subsequent measurement of debt issuance costs related to line-of-credit arrangements. The guidance allows an entity to present debt issuance costs related to a line-of-credit arrangement as an asset and subsequently amortize the deferred debt issuance costs ratably over the term of the line-of-credit arrangement, regardless of whether there are any outstanding borrowings under the line-of-credit arrangement. The April 2015 guidance and the August 2015 guidance are effective on a retrospective basis for annual reporting periods beginning after December 15, 2015, including interim periods within that reporting period. Early application is permitted. The April 2015 guidance and the August 2015 guidance are not expected to have a material impact on the Company’s results of operations or financial position, but will require changes to the presentation of the consolidated balance sheets and the notes to the consolidated financial statements.

ACQUISITIONS

9 Months Ended

Sep. 30, 2015

Business Combinations [Abstract]

ACQUISITION

ACQUISITIONS

Apartments.com

On February 28, 2014, the Company and Classified Ventures, LLC (“CV”) entered into an Asset Purchase Agreement (the “Asset Purchase Agreement”). Pursuant to the Asset Purchase Agreement, on April 1, 2014 (the “Closing Date”), the Company purchased from CV certain assets and assumed certain liabilities, in each case, related to the Apartments.com business (collectively referred to herein as “Apartments.com”). Apartments.com is a national online apartment rentals resource for renters, property managers and owners. Apartments.com offers renters a searchable database of apartment listings and provides professional property management companies and landlords with an advertising destination. Renters can conduct personalized searches of apartment listings and view video demonstrations and community reviews through the Apartments.com website and mobile applications. The Apartments.com network of rental websites also includes ApartmentHomeLiving.com, another national online apartment rentals resource. The acquisition increased the Company's presence in the multifamily vertical.

In consideration for the purchase of Apartments.com, on April 1, 2014, the Company paid $587.1 million in cash, including an estimated $2.1 million in connection with a preliminary net working capital adjustment as of the Closing Date. Pursuant to the terms of the Asset Purchase Agreement, the purchase price was reduced by approximately $2.9 million following the final determination of the net working capital of Apartments.com as of the Closing Date, and CV paid the Company $2.9 million on July 9, 2014.


3.	ACQUISITIONS — (CONTINUED)

Apartments.com — (Continued)

The Company applied the acquisition method to account for the Apartments.com 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):



Accounts receivable	$	11,402
Goodwill	421,724
Acquired trade names and other intangible assets	71,779
Acquired customer base	69,684
Acquired database technology	11,489
Acquired building photography	1,006
Other assets and liabilities	(2,866		)
Fair value of identifiable net assets acquired	$	584,218

The net assets of Apartments.com 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 consists of one distinct intangible asset, is composed of acquired customer contracts and the related customer relationships, and has an estimated useful life of ten years. The acquired database technology had an estimated useful life of one year due to the Company's intent to replace the acquired database technology, which occurred in February of 2015. The acquired trade names and other intangible assets have a weighted average estimated useful life of thirteen years. The acquired building photography has an estimated useful life of three years. 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 are 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 $421.7 million of goodwill recorded as part of the acquisition is associated with the Company's North America operating segment and the entire amount of goodwill is expected to be deductible for income tax purposes in future periods.

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 Apartments.com 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 Apartments.com's operations; and (ii) any intangible assets that do not qualify for separate recognition, such as the assembled workforce.

As a result of the acquisition of Apartments.com, the Company recorded approximately $1.4 million in acquisition-related costs for the nine months ended September 30, 2014. These costs include expenses directly related to acquiring Apartments.com, were expensed as incurred and were recorded in general and administrative expense. The Company did not record any acquisition-related costs as result of the acquisition of Apartments.com for the three months ended September 30, 2014. The Company did not record any acquisition-related costs as result of the acquisition of Apartments.com for the three and nine months ended September 30, 2015.

Apartment Finder

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 herein 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. The acquisition furthered the Company's expansion into the multifamily vertical.


3.	ACQUISITIONS — (CONTINUED)

Apartment Finder — (Continued)

In consideration for the purchase of Apartment Finder, on June 1, 2015, the Company paid $172.7 million in cash, including an estimated $2.7 million in connection with a preliminary net working capital adjustment as of the closing date. Pursuant to the terms of the agreement and plan of merger, 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 preliminary 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 has an estimated useful life of five months due to the Company's intent to replace the acquired database technology in 2015. The acquired trade names and other intangible assets have a weighted average estimated useful life of nine years. The acquired building photography has an estimated useful life of five months due to the Company's intent to replace the acquired building photographs in 2015. 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 are 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 $107.7 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. The purchase accounting is preliminary subject to the completion of the accounting for certain tax related items.

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.

- Definition

The entire disclosure for a business combination (or series of individually immaterial business combinations) completed during the period, including background, timing, and recognized assets and liabilities. The disclosure may include leverage buyout transactions (as applicable).

+ References

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-Name Accounting Standards Codification
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+ Details

INVESTMENTS

9 Months Ended

Sep. 30, 2015

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 long-term variable rate debt instruments with an auction reset feature, referred to as auction rate securities (“ARS”). Investments are carried at fair value.


4.	INVESTMENTS — (CONTINUED)

Scheduled maturities of investments classified as available-for-sale as of September 30, 2015 are as follows (in thousands):



Maturity	Fair Value
Due:
October 1, 2015 — September 30, 2016	$	—
October 1, 2016 — September 30, 2020	1,015
October 1, 2020 — September 30, 2025	—
After September 30, 2025	14,492
Available-for-sale investments	$	15,507

The Company had no realized gains on its investments for each of the three and nine months ended September 30, 2015 and 2014. The Company had no realized losses on its investments for each of the three and nine months ended September 30, 2015 and 2014. 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, 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	$	572	$	(1,007	)	$	15,507
Available-for-sale investments	$	15,942	$	572	$	(1,007	)	$	15,507

As of December 31, 2014, 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	$	17,842	$	380	$	(1,071	)	$	17,151
Available-for-sale investments	$	17,842	$	380	$	(1,071	)	$	17,151

The unrealized losses on the Company’s investments as of September 30, 2015 and December 31, 2014 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, 2015 and December 31, 2014. See Note 5 for further discussion of the fair value of the Company’s financial assets.


4.	INVESTMENTS — (CONTINUED)

The components of the Company’s investments in an unrealized loss position for twelve months or longer were as follows (in thousands):



	September 30, 2015					December 31, 2014
	Aggregate Fair Value		Gross Unrealized Losses			Aggregate Fair Value		Gross Unrealized Losses
Auction rate securities	$	14,492	$	(1,007	)	$	16,329	$	(1,071	)
Investments in an unrealized loss position	$	14,492	$	(1,007	)	$	16,329	$	(1,071	)

The Company did not have any investments in an unrealized loss position for less than twelve months as of September 30, 2015 and December 31, 2014.

- Definition

The entire disclosure for investments in certain debt and equity securities.

+ References + Details

FAIR VALUE

9 Months Ended

Sep. 30, 2015

Fair Value Disclosures [Abstract]

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, 2015 (in thousands):



	Level 1		Level 2		Level 3		Total
Assets:
Cash	$	358,625	$	—	$	—	$	358,625
Money market funds	5,180		—		—		5,180
Commercial paper	11,704		—		—		11,704
Auction rate securities	—		—		15,507		15,507
Total assets measured at fair value	$	375,509	$	—	$	15,507	$	391,016



	Level 1		Level 2		Level 3		Total
Assets:
Cash	$	160,275	$	—	$	—	$	160,275
Money market funds	310,482		—		—		310,482
Commercial paper	56,255		—		—		56,255
Auction rate securities	—		—		17,151		17,151
Total assets measured at fair value	$	527,012	$	—	$	17,151	$	544,163

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.


5.	FAIR VALUE — (CONTINUED)

The following tables summarize changes in fair value of the Company’s Level 3 assets for the three and nine months ended September 30, 2015 and 2014 (in thousands):



	Three Months Ended September 30,						Nine Months Ended September 30,
	2015			2014			2015			2014
Balance at beginning of period	$	16,049		$	21,639		$	17,151		$	21,990
Decrease in unrealized loss included in accumulated other comprehensive loss	8			42			256			241
Settlements	(550		)	(600		)	(1,900		)	(1,150		)
Balance at end of period	$	15,507		$	21,081		$	15,507		$	21,081

The following table summarizes changes in fair value of the Company’s Level 3 assets from December 31, 2007 to September 30, 2015 (in thousands):



	Auction Rate Securities
Balance at December 31, 2007	$	53,975
Increase in unrealized loss included in accumulated other comprehensive loss	(3,710		)
Settlements	(20,925		)
Balance at December 31, 2008	29,340
Decrease in unrealized loss included in accumulated other comprehensive loss	684
Settlements	(300		)
Balance at December 31, 2009	29,724
Decrease in unrealized loss included in accumulated other comprehensive loss	40
Settlements	(575		)
Balance at December 31, 2010	29,189
Decrease in unrealized loss included in accumulated other comprehensive loss	245
Settlements	(4,850		)
Balance at December 31, 2011	24,584
Auction rate securities upon acquisition	442
Decrease in unrealized loss included in accumulated other comprehensive loss	836
Settlements	(4,200		)
Balance at December 31, 2012	21,662
Decrease in unrealized loss included in accumulated other comprehensive loss	378
Settlements	(50		)
Balance at December 31, 2013	21,990
Decrease in unrealized loss included in accumulated other comprehensive loss	836
Settlements	(5,675		)
Balance at December 31, 2014	17,151
Decrease in unrealized loss included in accumulated other comprehensive loss	256
Settlements	(1,900		)
Balance at September 30, 2015	$	15,507

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.


5.	FAIR VALUE — (CONTINUED)

As of September 30, 2015, the Company held ARS with $16.8 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, these securities are classified as long-term investments in the Company’s condensed consolidated balance sheet as of September 30, 2015.

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, 2015. 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, 2015 and December 31, 2014 was approximately 4.4% and 4.1%, 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.

Based on this assessment of fair value, as of September 30, 2015, the Company determined there was a net decline in the fair value of its ARS investments of approximately $435,000. 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.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

GOODWILL

9 Months Ended

Sep. 30, 2015

Goodwill [Abstract]

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, 2013	$	692,639	$	25,948		$	718,587
Acquisition	421,724		—			421,724
Effect of foreign currency translation	—		(1,506		)	(1,506		)
Goodwill, December 31, 2014	1,114,363		24,442			1,138,805
Acquisitions	109,305		2,400			111,705
Effect of foreign currency translation	—		(565		)	(565		)
Goodwill, September 30, 2015	$	1,223,668	$	26,277		$	1,249,945


6.	GOODWILL — (CONTINUED)

The Company recorded goodwill of approximately $421.7 million in connection with the April 1, 2014 acquisition of Apartments.com. The Company recorded goodwill of approximately $107.7 million in connection with the June 1, 2015 acquisition of Apartment Finder and recorded goodwill of approximately $2.4 million in connection with the July 1, 2015 acquisition of the assets of Belbex Corporate, S.L., a small commercial real estate information provider operating in Madrid, Spain. Additionally, the Company recorded goodwill of approximately $1.6 million during the three months ended September 30, 2015 in connection with the acquisition of certain assets related to the business operations of Apartment Finder's independent distributors within various markets.

INTANGIBLE ASSETS

9 Months Ended

Sep. 30, 2015

Intangible Assets, Net (Excluding Goodwill) [Abstract]

INTANGIBLE ASSETS

Intangible assets consist of the following (in thousands, except amortization period data):



	September 30, 2015			December 31, 2014			Weighted- Average Amortization Period (in years)
Capitalized product development cost	$	2,243		$	2,140		4
Accumulated amortization	(2,163		)	(2,140		)
Capitalized product development cost, net	80			—

Building photography	17,649			14,943			4
Accumulated amortization	(15,217		)	(12,665		)
Building photography, net	2,432			2,278

Acquired database technology	81,898			88,739			5
Accumulated amortization	(63,226		)	(60,498		)
Acquired database technology, net	18,672			28,241

Acquired customer base	220,760			199,826			10
Accumulated amortization	(123,409		)	(102,443		)
Acquired customer base, net	97,351			97,383

Acquired trade names and other intangible assets ⁽¹⁾	154,266			128,171			12
Accumulated amortization	(21,988		)	(14,451		)
Acquired trade names and other intangible assets, net	132,278			113,720

Intangible assets, net	$	250,813		$	241,622

⁽¹⁾ The weighted-average amortization period for acquired trade names excludes $48.7 million for acquired trade names recorded in connection with the LoopNet acquisition on April 30, 2012, which amount is not amortized, but is subject to annual impairment tests.

In February 2015, as a result of the Company's product development efforts, it launched a new 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 $1.4 million in cost of revenues in the condensed consolidated statements of operations within the Company's North America operating segment for the three months ended March 31, 2015.


7.	INTANGIBLE ASSETS — (CONTINUED)

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 $1.4 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 three months ended June 30, 2015.

LONG-TERM DEBT

9 Months Ended

Sep. 30, 2015

Long-term Debt, Current and Noncurrent [Abstract]

LONG-TERM DEBT

On April 1, 2014, 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 $400.0 million term loan facility and a $225.0 million revolving credit facility, each with a term of five years. The proceeds of the term loan facility and the initial borrowing of $150.0 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 $150.0 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 $148.8 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 $10.0 million, and up to $10.0 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 2.00% 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 0.50% and (z) LIBOR for a one-month interest period plus 1.00%, plus an initial spread of 1.00% 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 2.00% 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 4.00 to 1.00 during each full fiscal quarter after the Closing Date through the three months ended March 31, 2016, and 3.50 to 1.00 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 5.00 to 1.00 during each full fiscal quarter after the Closing Date through the three months ended March 31, 2016, and 4.50 to 1.00 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, 2015.


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 $10.1 million in debt issuance costs as of April 1, 2014. The debt issuance costs were comprised of approximately $9.7 million in underwriting fees and approximately $400,000 primarily related to legal fees associated with the debt issuance. Approximately $10.0 million of the fees associated with the refinancing, 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, 2015 and December 31, 2014, no amounts were outstanding under the revolving credit facility. Total interest expense for the term loan facility and revolving credit facility was approximately $2.4 million and $2.7 million for the three months ended September 30, 2015 and 2014, respectively. Total interest expense for the term loan facility and revolving credit facility was approximately $7.1 million and $8.1 million for the nine months ended September 30, 2015 and 2014, respectively. Interest expense included amortized debt issuance costs of approximately $830,000 and $904,000 for the three months ended September 30, 2015 and 2014, respectively. Interest expense included amortized debt issuance costs of approximately $2.5 million for each of the nine months ended September 30, 2015 and 2014. Total interest paid for the term loan facility was approximately $1.5 million and $1.7 million for the three months ended September 30, 2015 and 2014, respectively. Total interest paid for the term loan facility was approximately $4.6 million and $5.4 million for the nine months ended September 30, 2015 and 2014, respectively.

INCOME TAXES	9 Months Ended
INCOME TAXES	Sep. 30, 2015
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The income tax provision for the nine months ended September 30, 2015 and 2014 reflects an effective tax rate of approximately 14% and 38%, 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	9 Months Ended
COMMITMENTS AND CONTINGENCIES	Sep. 30, 2015
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 $400.0 million term loan facility and a $225.0 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

9 Months Ended

Sep. 30, 2015

Segment Reporting [Abstract]

SEGMENT REPORTING

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 parts of Canada, and International, which includes the U.K., Madrid, Spain and parts of 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^TMservices. 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, CoStarGo®. 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 EBITDA, which is the Company’s net income (loss) before interest, income taxes, depreciation and amortization. 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 September 30,						Nine Months Ended September 30,
	2015			2014			2015			2014
Revenues
North America	$	182,556		$	146,899		$	500,059		$	402,074
International
External customers	6,522			6,157			18,696			17,766
Intersegment revenue	4			5			25			41
Total International revenue	6,526			6,162			18,721			17,807
Intersegment eliminations	(4		)	(5		)	(25		)	(41		)
Total revenues	$	189,078		$	153,056		$	518,755		$	419,840

EBITDA
North America	$	20,993		$	42,929		$	32,816		$	106,387
International	1,096			763			2,124			1,876
Total EBITDA	$	22,089		$	43,692		$	34,940		$	108,263

The reconciliation of EBITDA to net income (loss) consists of the following (in thousands):



	Three Months Ended September 30,						Nine Months Ended September 30,
	2015			2014			2015			2014
EBITDA	$	22,089		$	43,692		$	34,940		$	108,263
Purchase amortization in cost of revenues	(9,964		)	(7,790		)	(22,887		)	(18,547		)
Purchase amortization in operating expenses	(7,153		)	(8,361		)	(21,260		)	(20,696		)
Depreciation and other amortization	(5,403		)	(4,061		)	(14,860		)	(11,490		)
Interest income	42			46			473			245
Interest expense	(2,363		)	(2,698		)	(7,060		)	(8,066		)
Income tax benefit (expense), net	(2,610		)	(7,871		)	4,199			(18,763		)
Net income (loss)	$	(5,362	)	$	12,957		$	(26,455	)	$	30,946


11.	SEGMENT REPORTING — (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 $225,000 and $204,000 for the three months ended September 30, 2015 and 2014, respectively. North America EBITDA includes an allocation of approximately $763,000 and $939,000 for the nine months ended September 30, 2015 and 2014, 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 $74,000 and $59,000 for the three months ended September 30, 2015 and 2014, respectively. International EBITDA includes a corporate allocation of approximately $200,000 and $197,000 for the nine months ended September 30, 2015 and 2014, respectively. This corporate allocation represents costs incurred for North America employees involved in management and expansion activities of the Company’s International operating segment.

Summarized information by operating segment consists of the following (in thousands):



	September 30, 2015			December 31, 2014
Property and equipment, net
North America	$	85,236		$	71,209
International	2,391			2,544
Total property and equipment, net	$	87,627		$	73,753

Goodwill
North America	$	1,223,668		$	1,114,363
International	26,277			24,442
Total goodwill	$	1,249,945		$	1,138,805

Assets
North America	$	2,141,822		$	2,138,768
International	40,930			41,896
Total operating segment assets	$	2,182,752		$	2,180,664

Reconciliation of operating segment assets to total assets
Total operating segment assets	$	2,182,752		$	2,180,664
Investment in subsidiaries	(18,344		)	(18,344		)
Intersegment receivables	(73,672		)	(78,638		)
Total assets	$	2,090,736		$	2,083,682

Liabilities
North America	$	571,465		$	564,832
International	73,099			75,584
Total operating segment liabilities	$	644,564		$	640,416

Reconciliation of operating segment liabilities to total liabilities
Total operating segment liabilities	$	644,564		$	640,416
Intersegment payables	(63,786		)	(70,280		)
Total liabilities	$	580,778		$	570,136

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

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+ Details

EQUITY OFFERING	9 Months Ended
EQUITY OFFERING	Sep. 30, 2015
Proceeds from (Repurchase of) Equity [Abstract]
EQUITY OFFERING	EQUITY OFFERING During June 2014, the Company completed a public equity offering of 3,450,000 shares of common stock for $160.00 per share. Net proceeds from the public equity offering were approximately $529.4 million, after deducting approximately $22.1 million of underwriting discounts and commissions and offering expenses of approximately $500,000. The Company has used and intends to continue to use the net proceeds from the sale of the securities to fund all or a portion of the costs of any strategic acquisitions it determines to pursue, to finance the growth of its business and for general corporate purposes. General corporate purposes may include additions to working capital, capital expenditures, repayment of debt, investments in the Company’s subsidiaries, possible acquisitions and the repurchase, redemption or retirement of securities, including the Company’s common stock.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Section E

Reference 15: http://www.xbrl.org/2003/role/presentationRef
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+ Details

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	Sep. 30, 2015
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, 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.
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. 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. Stock options to purchase approximately 80,000 shares that were outstanding for the three and nine months ended September 30, 2014 were not included in the computation of diluted net income per share because the exercise price of the stock options was greater than the average market share price of the common stock during the period. Additionally, shares underlying restricted common stock awards and restricted stock units that vest based on Company performance and/or 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. 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. 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 fair value of 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. 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, 2014, including the expected dates of adoption and estimated effects on the Company’s condensed consolidated financial statements, except for the following: 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 U.S. GAAP and International Financial Reporting Standards (“IFRS”). This guidance provides a more robust framework for addressing revenue issues, improves the comparability of revenue recognition practices across industries, provides more 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 goods 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. 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. The original effective date of the new standard was for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. In August 2015, the FASB issued an accounting standards update that defers by one year the effective date of this new revenue recognition standard. As a result, the new standard will be effective for annual reporting periods beginning after December 15, 2017, with an option that permits companies to adopt the standard as early as the original effective date. Early application prior to the original effective date is not permitted. The Company has not yet determined when it will adopt the standard and it has not selected a transition method and is currently evaluating the impact this guidance will have on its financial statements. In April 2015, the FASB issued authoritative guidance to simplify the presentation of debt issuance costs. This guidance requires a company to present debt issuance costs related to a recognized debt liability in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by this guidance. In August 2015, the FASB issued an accounting standards update to address the presentation and subsequent measurement of debt issuance costs related to line-of-credit arrangements. The guidance allows an entity to present debt issuance costs related to a line-of-credit arrangement as an asset and subsequently amortize the deferred debt issuance costs ratably over the term of the line-of-credit arrangement, regardless of whether there are any outstanding borrowings under the line-of-credit arrangement. The April 2015 guidance and the August 2015 guidance are effective on a retrospective basis for annual reporting periods beginning after December 15, 2015, including interim periods within that reporting period. Early application is permitted. The April 2015 guidance and the August 2015 guidance are not expected to have a material impact on the Company’s results of operations or financial position, but will require changes to the presentation of the consolidated balance sheets and the notes to the consolidated financial statements.

ACQUISITIONS (Policies)	9 Months Ended
ACQUISITIONS (Policies)	Sep. 30, 2015
Business Acquisition [Line Items]
Acquisitions	Business Combinations The Company allocates the fair value of 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. Upon the conclusion of the measurement period, any subsequent adjustments are recorded to earnings.
Apartments.com [Member]
Business Acquisition [Line Items]
Acquisitions	The Company applied the acquisition method to account for the Apartments.com transaction, which requires that, among other things, assets acquired and liabilities assumed be recorded at their fair values as of the acquisition date.
Apartment Finder [Member]
Business Acquisition [Line Items]
Acquisitions	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)	9 Months Ended
INVESTMENTS (Policies)	Sep. 30, 2015
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 long-term variable rate debt instruments with an auction reset feature, referred to as auction rate securities (“ARS”). Investments are carried at fair value.

- Definition

Disclosure of accounting policy for investments in financial assets, including marketable securities (debt and equity securities with readily determinable fair values), investments accounted for under the equity method and cost method, securities borrowed and loaned, and repurchase and resale agreements. For marketable securities, the disclosure may include the entity's accounting treatment for transfers between investment categories and how the fair values for such securities are determined. Also, for all investments, an entity may describe its policy for assessing, recognizing and measuring impairment of the investment.

+ References + Details

COMMITMENTS AND CONTINGENCIES (Policies)	9 Months Ended
COMMITMENTS AND CONTINGENCIES (Policies)	Sep. 30, 2015
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 ACCOUNTING POLICIES (Tables)

9 Months Ended

Sep. 30, 2015

Accounting Policies [Abstract]

Schedule of accumulated other comprehensive loss

The components of accumulated other comprehensive loss were as follows (in thousands):



	September 30, 2015			December 31, 2014
Foreign currency translation adjustment	$	(6,412	)	$	(5,693	)
Accumulated net unrealized loss on investments, net of tax	(435		)	(691		)
Total accumulated other comprehensive loss	$	(6,847	)	$	(6,384	)

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 September 30,					Nine Months Ended September 30,
Numerator:	2015			2014		2015			2014
Numerator:
Net income (loss)	$	(5,362	)	$	12,957	$	(26,455	)	$	30,946
Denominator:
Denominator for basic net income (loss) per share — weighted-average outstanding shares	31,980			31,742		31,934			29,692
Effect of dilutive securities:
Stock options and restricted stock	—			333		—			442
Denominator for diluted net income (loss) per share — weighted-average outstanding shares	31,980			32,075		31,934			30,134

Net income (loss) per share — basic	$	(0.17	)	$	0.41	$	(0.83	)	$	1.04
Net income (loss) per share — diluted	$	(0.17	)	$	0.40	$	(0.83	)	$	1.03

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 September 30,		Nine Months Ended September 30,
	2015	2014	2015	2014
Performance-based restricted stock awards	55	23	55	23
Service-based restricted stock units	1	1	1	1
Total shares excluded from computation	56	24	56	24

Stock-based compensation expense for stock options and restricted stock



	Three Months Ended September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014
Cost of revenues	$	1,533	$	1,067	$	4,242	$	3,331
Selling and marketing	1,411		954		3,595		2,729
Software development	1,602		1,179		4,318		3,867
General and administrative	4,766		3,447		13,014		10,979
Total stock-based compensation	$	9,312	$	6,647	$	25,169	$	20,906

ACQUISITIONS (Tables)

9 Months Ended

Sep. 30, 2015

Apartments.com [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):



Accounts receivable	$	11,402
Goodwill	421,724
Acquired trade names and other intangible assets	71,779
Acquired customer base	69,684
Acquired database technology	11,489
Acquired building photography	1,006
Other assets and liabilities	(2,866		)
Fair value of identifiable net assets acquired	$	584,218

Apartment Finder [Member]

Business Acquisition [Line Items]

Schedule of assets acquired and liabilities assumed

The following table summarizes the preliminary 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)

9 Months Ended

Sep. 30, 2015

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, 2015 are as follows (in thousands):



Maturity	Fair Value
Due:
October 1, 2015 — September 30, 2016	$	—
October 1, 2016 — September 30, 2020	1,015
October 1, 2020 — September 30, 2025	—
After September 30, 2025	14,492
Available-for-sale investments	$	15,507

Schedule of available for sale securities reconciliation

As of September 30, 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	$	572	$	(1,007	)	$	15,507
Available-for-sale investments	$	15,942	$	572	$	(1,007	)	$	15,507

As of December 31, 2014, 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	$	17,842	$	380	$	(1,071	)	$	17,151
Available-for-sale investments	$	17,842	$	380	$	(1,071	)	$	17,151

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, 2015					December 31, 2014
	Aggregate Fair Value		Gross Unrealized Losses			Aggregate Fair Value		Gross Unrealized Losses
Auction rate securities	$	14,492	$	(1,007	)	$	16,329	$	(1,071	)
Investments in an unrealized loss position	$	14,492	$	(1,007	)	$	16,329	$	(1,071	)

FAIR VALUE (Tables)

9 Months Ended

Sep. 30, 2015

Fair Value Disclosures [Abstract]

Summary of fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis



	Level 1		Level 2		Level 3		Total
Assets:
Cash	$	358,625	$	—	$	—	$	358,625
Money market funds	5,180		—		—		5,180
Commercial paper	11,704		—		—		11,704
Auction rate securities	—		—		15,507		15,507
Total assets measured at fair value	$	375,509	$	—	$	15,507	$	391,016



	Level 1		Level 2		Level 3		Total
Assets:
Cash	$	160,275	$	—	$	—	$	160,275
Money market funds	310,482		—		—		310,482
Commercial paper	56,255		—		—		56,255
Auction rate securities	—		—		17,151		17,151
Total assets measured at fair value	$	527,012	$	—	$	17,151	$	544,163

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, 2015 and 2014 (in thousands):



	Three Months Ended September 30,						Nine Months Ended September 30,
	2015			2014			2015			2014
Balance at beginning of period	$	16,049		$	21,639		$	17,151		$	21,990
Decrease in unrealized loss included in accumulated other comprehensive loss	8			42			256			241
Settlements	(550		)	(600		)	(1,900		)	(1,150		)
Balance at end of period	$	15,507		$	21,081		$	15,507		$	21,081

The following table summarizes changes in fair value of the Company’s Level 3 assets from December 31, 2007 to September 30, 2015 (in thousands):



	Auction Rate Securities
Balance at December 31, 2007	$	53,975
Increase in unrealized loss included in accumulated other comprehensive loss	(3,710		)
Settlements	(20,925		)
Balance at December 31, 2008	29,340
Decrease in unrealized loss included in accumulated other comprehensive loss	684
Settlements	(300		)
Balance at December 31, 2009	29,724
Decrease in unrealized loss included in accumulated other comprehensive loss	40
Settlements	(575		)
Balance at December 31, 2010	29,189
Decrease in unrealized loss included in accumulated other comprehensive loss	245
Settlements	(4,850		)
Balance at December 31, 2011	24,584
Auction rate securities upon acquisition	442
Decrease in unrealized loss included in accumulated other comprehensive loss	836
Settlements	(4,200		)
Balance at December 31, 2012	21,662
Decrease in unrealized loss included in accumulated other comprehensive loss	378
Settlements	(50		)
Balance at December 31, 2013	21,990
Decrease in unrealized loss included in accumulated other comprehensive loss	836
Settlements	(5,675		)
Balance at December 31, 2014	17,151
Decrease in unrealized loss included in accumulated other comprehensive loss	256
Settlements	(1,900		)
Balance at September 30, 2015	$	15,507

GOODWILL (Tables)

9 Months Ended

Sep. 30, 2015

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, 2013	$	692,639	$	25,948		$	718,587
Acquisition	421,724		—			421,724
Effect of foreign currency translation	—		(1,506		)	(1,506		)
Goodwill, December 31, 2014	1,114,363		24,442			1,138,805
Acquisitions	109,305		2,400			111,705
Effect of foreign currency translation	—		(565		)	(565		)
Goodwill, September 30, 2015	$	1,223,668	$	26,277		$	1,249,945

INTANGIBLE ASSETS (Tables)

9 Months Ended

Sep. 30, 2015

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, 2015			December 31, 2014			Weighted- Average Amortization Period (in years)
Capitalized product development cost	$	2,243		$	2,140		4
Accumulated amortization	(2,163		)	(2,140		)
Capitalized product development cost, net	80			—

Building photography	17,649			14,943			4
Accumulated amortization	(15,217		)	(12,665		)
Building photography, net	2,432			2,278

Acquired database technology	81,898			88,739			5
Accumulated amortization	(63,226		)	(60,498		)
Acquired database technology, net	18,672			28,241

Acquired customer base	220,760			199,826			10
Accumulated amortization	(123,409		)	(102,443		)
Acquired customer base, net	97,351			97,383

Acquired trade names and other intangible assets ⁽¹⁾	154,266			128,171			12
Accumulated amortization	(21,988		)	(14,451		)
Acquired trade names and other intangible assets, net	132,278			113,720

Intangible assets, net	$	250,813		$	241,622

SEGMENT REPORTING (Tables)

9 Months Ended

Sep. 30, 2015

Segment Reporting [Abstract]

Summarized information by operating segment

Summarized information by operating segment consists of the following (in thousands):



	Three Months Ended September 30,						Nine Months Ended September 30,
	2015			2014			2015			2014
Revenues
North America	$	182,556		$	146,899		$	500,059		$	402,074
International
External customers	6,522			6,157			18,696			17,766
Intersegment revenue	4			5			25			41
Total International revenue	6,526			6,162			18,721			17,807
Intersegment eliminations	(4		)	(5		)	(25		)	(41		)
Total revenues	$	189,078		$	153,056		$	518,755		$	419,840

EBITDA
North America	$	20,993		$	42,929		$	32,816		$	106,387
International	1,096			763			2,124			1,876
Total EBITDA	$	22,089		$	43,692		$	34,940		$	108,263

Reconciliation of EBITDA to net income (loss)

The reconciliation of EBITDA to net income (loss) consists of the following (in thousands):



	Three Months Ended September 30,						Nine Months Ended September 30,
	2015			2014			2015			2014
EBITDA	$	22,089		$	43,692		$	34,940		$	108,263
Purchase amortization in cost of revenues	(9,964		)	(7,790		)	(22,887		)	(18,547		)
Purchase amortization in operating expenses	(7,153		)	(8,361		)	(21,260		)	(20,696		)
Depreciation and other amortization	(5,403		)	(4,061		)	(14,860		)	(11,490		)
Interest income	42			46			473			245
Interest expense	(2,363		)	(2,698		)	(7,060		)	(8,066		)
Income tax benefit (expense), net	(2,610		)	(7,871		)	4,199			(18,763		)
Net income (loss)	$	(5,362	)	$	12,957		$	(26,455	)	$	30,946

Summarized information by operating segment, assets and liabilities

Summarized information by operating segment consists of the following (in thousands):



	September 30, 2015			December 31, 2014
Property and equipment, net
North America	$	85,236		$	71,209
International	2,391			2,544
Total property and equipment, net	$	87,627		$	73,753

Goodwill
North America	$	1,223,668		$	1,114,363
International	26,277			24,442
Total goodwill	$	1,249,945		$	1,138,805

Assets
North America	$	2,141,822		$	2,138,768
International	40,930			41,896
Total operating segment assets	$	2,182,752		$	2,180,664

Reconciliation of operating segment assets to total assets
Total operating segment assets	$	2,182,752		$	2,180,664
Investment in subsidiaries	(18,344		)	(18,344		)
Intersegment receivables	(73,672		)	(78,638		)
Total assets	$	2,090,736		$	2,083,682

Liabilities
North America	$	571,465		$	564,832
International	73,099			75,584
Total operating segment liabilities	$	644,564		$	640,416

Reconciliation of operating segment liabilities to total liabilities
Total operating segment liabilities	$	644,564		$	640,416
Intersegment payables	(63,786		)	(70,280		)
Total liabilities	$	580,778		$	570,136

ORGANIZATION (Details)	9 Months Ended
ORGANIZATION (Details)	Sep. 30, 2015 operating_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 ACCOUNTING POLICIES SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, ADVERTISING COSTS (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accounting Policies [Abstract]
Advertising expense	$ 33.5	$ 8.7	$ 112.5	$ 20.2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, FOREIGN CURRENCY AND ACCUMULATED OTHER COMPREHENSIVE LOSS, NET OF TAX (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
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	(6,412)		(6,412)		$ (5,693)
Accumulated net unrealized loss on investments, net of tax	(435)		(435)		(691)
Total accumulated other comprehensive loss	(6,847)		(6,847)		$ (6,384)
Reclassification out of accumulated other comprehensive loss	$ 0	$ 0	$ 0	$ 0

- Definition

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

+ References + Details

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, NET INCOME (LOSS) PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	56,000	24,000	56,000	24,000
Numerator: [Abstract]
Net income (loss)	$ (5,362)	$ 12,957	$ (26,455)	$ 30,946
Denominator: [Abstract]
Denominator for basic net income (loss) per share - weighted-average outstanding shares (in shares)	31,980,000	31,742,000	31,934,000	29,692,000
Effect of dilutive securities: [Abstract]
Stock options and restricted stock	0	333,000	0	442,000
Denominator for diluted net income (loss) per share - weighted-average outstanding shares (in shares)	31,980,000	32,075,000	31,934,000	30,134,000
Net income (loss) per share - basic (in dollars per share)	$ (0.17)	$ 0.41	$ (0.83)	$ 1.04
Net income (loss) per share - diluted (in dollars per share)	$ (0.17)	$ 0.40	$ (0.83)	$ 1.03
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		80,000		80,000
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	55,000	23,000	55,000	23,000
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	1,000	1,000	1,000	1,000

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, STOCK BASED COMPENSATION EXPENSE (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Stock-Based Compensation Expense [Abstract]
Net cash proceeds from the exercise of stock options and Employee Stock Purchase Plan	$ 646	$ 1,610	$ 5,350	$ 5,157
Excess tax benefits realized from stock option exercised and restricted stock awards vested	418	1,348	7,970	28,167
Compensation expense	$ 9,312	$ 6,647	$ 25,169	$ 20,906
Exercise of stock options (in shares)	0	20,366	41,068	66,201
Cost of Revenues [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	$ 1,533	$ 1,067	$ 4,242	$ 3,331
Selling and Marketing [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	1,411	954	3,595	2,729
Software Development [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	1,602	1,179	4,318	3,867
General and Administrative [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	$ 4,766	$ 3,447	$ 13,014	$ 10,979

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, DEBT ISSUANCE COSTS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Apr. 01, 2014
Deferred Finance Costs, Own-share Lending Arrangement, Issuance Costs, Net [Abstract]
Capitalized debt issuance costs	$ 10,713		$ 10,713		$ 13,199	$ 10,000
Amortization of debt issuance costs	$ 830	$ 904	$ 2,486	$ 2,459

ACQUISITIONS (Details for Apartments.com) $ in Thousands			3 Months Ended		9 Months Ended
ACQUISITIONS (Details for Apartments.com) $ in Thousands	Jun. 01, 2015 USD ($) distinct_intangible_asset	Apr. 02, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Apr. 01, 2014 USD ($) distinct_intangible_asset	Dec. 31, 2013 USD ($)
Business Acquisition [Line Items]
Goodwill			$ 1,249,945		$ 1,249,945		$ 1,138,805		$ 718,587
Apartments.com [Member]
Business Acquisition [Line Items]
Payments to acquire businesses		$ 587,104
Closing purchase price adjustments		2,104
Post closing purchase price adjustments		$ 2,886
Goodwill								$ 421,724
Goodwill tax deductible amount								$ 421,724
Business combination, acquisition related costs			$ 0	$ 0	$ 0	$ 1,375
Apartment Finder [Member]
Business Acquisition [Line Items]
Payments to acquire businesses	$ 172,706
Closing purchase price adjustments	2,706
Post closing purchase price adjustments	21
Goodwill	107,692
Goodwill tax deductible amount	$ 0
Customer Contracts [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets					10 years
Customer Contracts [Member] \| Apartments.com [Member]
Business Acquisition [Line Items]
Number of distinct intangible assets \| distinct_intangible_asset								1
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] \| Apartments.com [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets		1 year
Developed Technology Rights [Member] \| Apartment Finder [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets	5 months
Trade Names and Other Intangible Assets [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets					12 years
Trade Names and Other Intangible Assets [Member] \| Apartments.com [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
Building Photography [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets					4 years
Building Photography [Member] \| Apartments.com [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets		3 years
Building Photography [Member] \| Apartment Finder [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets	5 months

ACQUISITIONS (Details - Schedule of Assets Acquired and Liabilities Assumed for Apartments.com) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Apr. 01, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Goodwill	$ 1,249,945	$ 1,138,805		$ 718,587
Apartments.com [Member]
Business Acquisition [Line Items]
Accounts receivable			$ 11,402
Goodwill			421,724
Other assets and liabilities			(2,866)
Fair value of identifiable net assets acquired			584,218
Apartments.com [Member] \| Trade Names and Other Intangible Assets [Member]
Business Acquisition [Line Items]
Intangible assets, other than goodwill			71,779
Apartments.com [Member] \| Customer Contracts [Member]
Business Acquisition [Line Items]
Intangible assets, other than goodwill			69,684
Apartments.com [Member] \| Developed Technology Rights [Member]
Business Acquisition [Line Items]
Intangible assets, other than goodwill			11,489
Apartments.com [Member] \| Building Photography [Member]
Business Acquisition [Line Items]
Intangible assets, other than goodwill			$ 1,006

ACQUISITIONS (Details for Apartment Finder) $ in Thousands		9 Months Ended
ACQUISITIONS (Details for Apartment Finder) $ in Thousands	Jun. 01, 2015 USD ($) distinct_intangible_asset	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Business Acquisition [Line Items]
Goodwill		$ 1,249,945	$ 1,138,805	$ 718,587
Apartment Finder [Member]
Business Acquisition [Line Items]
Percentage of outstanding stock acquired by the Company	100.00%
Payments to acquire businesses	$ 172,706
Closing purchase price adjustments	2,706
Post closing purchase price adjustments	21
Goodwill	107,692
Goodwill tax deductible amount	$ 0
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
Trade Names and Other Intangible Assets [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets		12 years
Trade Names and Other Intangible Assets [Member] \| Apartment Finder [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets	9 years
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

ACQUISITIONS (Details - Schedule of Assets Acquired and Liabilities Assumed for Apartment Finder) - USD ($) $ in Thousands	Sep. 30, 2015	Jun. 01, 2015	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Goodwill	$ 1,249,945		$ 1,138,805	$ 718,587
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 MATURITIES AND REALIZED GAINS AND LOSSES (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, gross realized gains	$ 0	$ 0	$ 0	$ 0
Available-for-sale securities, gross realized losses	0	$ 0	0	$ 0
Debt Maturities Fair Value [Abstract]
October 1, 2015 — September 30, 2016	0		0
October 1, 2016 — September 30, 2020	1,015,000		1,015,000
October 1, 2020 — September 30, 2025	0		0
After September 30, 2025	14,492,000		14,492,000
Fair Value	$ 15,507,000		$ 15,507,000		$ 17,151,000

INVESTMENTS, AVAILABLE-FOR-SALE SECURITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, continuous unrealized loss position, less than 12 months, accumulated loss	$ 0	$ 0
Available-for-sale Securities Reconciliation [Abstract]
Amortized Cost	15,942	17,842
Gross Unrealized Gains	572	380
Gross Unrealized Losses	1,007	1,071
Fair Value	15,507	17,151
Available-for-sale securities, unrealized loss positions
Aggregate Fair Value	14,492	16,329
Auction Rate Securities [Member]
Available-for-sale Securities Reconciliation [Abstract]
Amortized Cost	15,942	17,842
Gross Unrealized Gains	572	380
Gross Unrealized Losses	1,007	1,071
Fair Value	15,507	17,151
Available-for-sale securities, unrealized loss positions
Aggregate Fair Value	$ 14,492	$ 16,329

FAIR VALUE (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
FAIR VALUE (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Unobservable inputs assets (level 3) [Roll forward]
Beginning balance	$ 16,049	$ 21,639	$ 17,151	$ 21,990	$ 21,990
Change in unrealized gain (loss) included in accumulated other comprehensive loss	8	42	256	241
Settlements	(550)	(600)	(1,900)	(1,150)
Ending balance	15,507	$ 21,081	$ 15,507	21,081	17,151	$ 21,990
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	16,750		$ 16,750
Temporary impairment of the auction rates security investments, net of unrealized gain	(435)		(435)		(691)
Fair Value, Measurements, Recurring [Member]
Assets:
Total assets measured at fair value	391,016		391,016		544,163
Fair Value, Measurements, Recurring [Member] \| Cash [Member]
Assets:
Total assets measured at fair value	358,625		358,625		160,275
Fair Value, Measurements, Recurring [Member] \| Money Market Funds [Member]
Assets:
Total assets measured at fair value	5,180		5,180		310,482
Fair Value, Measurements, Recurring [Member] \| Commercial Paper [Member]
Assets:
Total assets measured at fair value	11,704		11,704		56,255
Fair Value, Measurements, Recurring [Member] \| Auction Rate Securities [Member]
Assets:
Total assets measured at fair value	15,507		15,507		17,151
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Assets:
Total assets measured at fair value	375,509		375,509		527,012
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Cash [Member]
Assets:
Total assets measured at fair value	358,625		358,625		160,275
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Money Market Funds [Member]
Assets:
Total assets measured at fair value	5,180		5,180		310,482
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Commercial Paper [Member]
Assets:
Total assets measured at fair value	11,704		11,704		56,255
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	15,507		15,507		17,151
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	15,507		15,507		17,151
Auction Rate Securities [Member]
Unobservable inputs assets (level 3) [Roll forward]
Beginning balance			17,151	$ 21,990	21,990	21,662	$ 24,584	$ 29,189	$ 29,724	$ 29,340	$ 53,975
Change in unrealized gain (loss) included in accumulated other comprehensive loss			256		836	378	836	245	40	684	(3,710)
Settlements			(1,900)		(5,675)	(50)	(4,200)	(4,850)	(575)	(300)	(20,925)
Auction rate securities upon acquisition							442
Ending balance	$ 15,507		$ 15,507		$ 17,151	$ 21,990	$ 21,662	$ 24,584	$ 29,189	$ 29,724	$ 29,340
Discount rate (in percent)			4.40%		4.10%

GOODWILL (Details) - USD ($) $ in Thousands				3 Months Ended	9 Months Ended	12 Months Ended
GOODWILL (Details) - USD ($) $ in Thousands	Jul. 01, 2015	Jun. 01, 2015	Apr. 02, 2014	Sep. 30, 2015	Sep. 30, 2015	Dec. 31, 2014
Goodwill [Roll Forward]
Goodwill, beginning balance					$ 1,138,805	$ 718,587
Acquisition					111,705	421,724
Effect of foreign currency translation					(565)	(1,506)
Goodwill, ending balance				$ 1,249,945	1,249,945	1,138,805
Apartments.com [Member]
Goodwill [Line Items]
Goodwill, period increase			$ 421,724
Apartment Finder [Member]
Goodwill [Line Items]
Goodwill, period increase		$ 107,692
Goodwill [Roll Forward]
Goodwill, ending balance		$ 107,692
Belbex [Member]
Goodwill [Line Items]
Goodwill, period increase	$ 2,400
Independent Distributor Buyout [Member]
Goodwill [Line Items]
Goodwill, period increase				1,613
North America [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance					1,114,363	692,639
Acquisition					109,305	421,724
Effect of foreign currency translation					0	0
Goodwill, ending balance				1,223,668	1,223,668	1,114,363
International [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance					24,442	25,948
Acquisition					2,400	0
Effect of foreign currency translation					(565)	(1,506)
Goodwill, ending balance				$ 26,277	$ 26,277	$ 24,442

INTANGIBLE ASSETS (Details) - USD ($)			3 Months Ended		9 Months Ended
INTANGIBLE ASSETS (Details) - USD ($)	Jun. 01, 2015	Apr. 02, 2014	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Apr. 30, 2012
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net					$ 250,813,000		$ 241,622,000
Impairment of intangible assets, finite-lived					2,778,000	$ 1,799,000
Capitalized Product Development Costs [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross					2,243,000		2,140,000
Finite-lived intangible assets, accumulated amortization					(2,163,000)		(2,140,000)
Finite-lived intangible assets, net					$ 80,000		0
Weighted-average amortization period (in years}					4 years
Building Photography [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross					$ 17,649,000		14,943,000
Finite-lived intangible assets, accumulated amortization					(15,217,000)		(12,665,000)
Finite-lived intangible assets, net					$ 2,432,000		2,278,000
Weighted-average amortization period (in years}					4 years
Developed Technology Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross					$ 81,898,000		88,739,000
Finite-lived intangible assets, accumulated amortization					(63,226,000)		(60,498,000)
Finite-lived intangible assets, net					$ 18,672,000		28,241,000
Weighted-average amortization period (in years}					5 years
Acquired Customer Base [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross					$ 220,760,000		199,826,000
Finite-lived intangible assets, accumulated amortization					(123,409,000)		(102,443,000)
Finite-lived intangible assets, net					$ 97,351,000		97,383,000
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					$ 154,266,000		128,171,000
Finite-lived intangible assets, accumulated amortization					(21,988,000)		(14,451,000)
Finite-lived intangible assets, net					$ 132,278,000		$ 113,720,000
Weighted-average amortization period (in years}					12 years
LoopNet [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Business acquisition, purchase price allocation, intangible assets not amortizable								$ 48,700,000
Apartments.com [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Impairment of intangible assets, finite-lived				$ 1,402,000
Apartments.com [Member] \| Building Photography [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}		3 years
Apartments.com [Member] \| Developed Technology Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}		1 year
Apartments.com [Member] \| Acquired Customer Base [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}		10 years
Apartments.com [Member] \| Trade Names and Other Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period (in years}		13 years
Apartment Finder [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Impairment of intangible assets, finite-lived			$ 1,376,000
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

LONG-TERM DEBT (Details) - USD ($)		1 Months Ended
LONG-TERM DEBT (Details) - USD ($)	Apr. 02, 2014	Jun. 30, 2014	Sep. 30, 2015	Dec. 31, 2014	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	$ 148,800,000
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.
Debt issuance costs	$ 10,100,000
Debt issuance underwriting fees	9,700,000
Debt Issuance Legal Fees	$ 400,000
Capitalized debt issuance costs			$ 10,713,000	$ 13,199,000	$ 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 (Details - Covenant Calculations)	Apr. 01, 2014
Debt Disclosure [Abstract]
Maximum first lien secured leverage ratio for first eight quarters after closing date	400.00%
Maximum first lien secured leverage ratio after eight quarters after closing date (in percent)	350.00%
Maximum total leverage ratio for first eight quarters after closing date (in percent)	500.00%
Maximum total leverage ratio after eight fiscal quarters (in percent)	450.00%

LONG-TERM DEBT (Details - Interest Expense and Amortization of Debt Issuance Costs) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Apr. 01, 2014
Debt Instrument [Line Items]
Line of credit facility, amount outstanding						$ 150,000
Interest expense, debt	$ 2,363	$ 2,698	$ 7,060	$ 8,066
Amortization of debt issuance costs	830	904	2,486	2,459
Interest paid	1,530	$ 1,720	4,571	$ 5,436
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, amount outstanding	$ 0		$ 0		$ 0

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References + Details

INCOME TAXES (Details)	9 Months Ended
INCOME TAXES (Details)	Sep. 30, 2015	Sep. 30, 2014
Income Tax Disclosure [Abstract]
Effective income tax rate (in percent)	14.00%	38.00%

COMMITMENTS AND CONTINGENCIES (Details) - CoStar Group [Member] - USD ($) $ in Millions	Apr. 02, 2014	Apr. 01, 2014
Term Loan [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity		$ 400.0
Term of loan (in years)	5 years
Revolving Credit Facility [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity		$ 225.0
Term of loan (in years)	5 years

SEGMENT REPORTING (Details)	3 Months Ended		9 Months Ended
SEGMENT REPORTING (Details)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) operating_segments	Sep. 30, 2014 USD ($)
Segment Reporting Information [Line Items]
Number of business segments (in segments) \| operating_segments			2
Segment Reporting Information, Revenue [Abstract]
Revenues	$ 189,078,000	$ 153,056,000	$ 518,755,000	$ 419,840,000
Reconciliation of EBITDA to net income (loss) [Abstract]
EBITDA	22,089,000	43,692,000	34,940,000	108,263,000
Purchase amortization in cost of revenues	(9,964,000)	(7,790,000)	(22,887,000)	(18,547,000)
Purchase amortization in operating expenses	(7,153,000)	(8,361,000)	(21,260,000)	(20,696,000)
Depreciation and other amortization	(5,403,000)	(4,061,000)	(14,860,000)	(11,490,000)
Interest income	42,000	46,000	473,000	245,000
Interest expense	(2,363,000)	(2,698,000)	(7,060,000)	(8,066,000)
Income tax benefit (expense), net	(2,610,000)	(7,871,000)	4,199,000	(18,763,000)
Net income (loss)	(5,362,000)	12,957,000	(26,455,000)	30,946,000
North America [Member]
Segment Reporting Information [Line Items]
North America corporate allocation	225,000	204,000	763,000	939,000
Segment Reporting Information, Revenue [Abstract]
Revenues	182,556,000	146,899,000	500,059,000	402,074,000
Reconciliation of EBITDA to net income (loss) [Abstract]
EBITDA	20,993,000	42,929,000	32,816,000	106,387,000
International [Member]
Segment Reporting Information [Line Items]
International corporate allocation	74,000	59,000	200,000	197,000
Segment Reporting Information, Revenue [Abstract]
Revenues	6,526,000	6,162,000	18,721,000	17,807,000
Reconciliation of EBITDA to net income (loss) [Abstract]
EBITDA	1,096,000	763,000	2,124,000	1,876,000
Intersegment Revenue [Member]
Segment Reporting Information, Revenue [Abstract]
Revenues	4,000	5,000	25,000	41,000
External Customers [Member]
Segment Reporting Information, Revenue [Abstract]
Revenues	6,522,000	6,157,000	18,696,000	17,766,000
Intersegment Eliminations [Member]
Segment Reporting Information, Revenue [Abstract]
Revenues	$ (4,000)	$ (5,000)	$ (25,000)	$ (41,000)

SEGMENT REPORTING, ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Property and equipment, net	$ 87,627	$ 73,753
Goodwill	1,249,945	1,138,805	$ 718,587
Reconciliation of operating segment assets to total assets [Abstract]
Total assets	2,090,736	2,083,682
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total liabilities	580,778	570,136
North America [Member]
Segment Reporting Information [Line Items]
Property and equipment, net	85,236	71,209
Goodwill	1,223,668	1,114,363	$ 692,639
International [Member]
Segment Reporting Information [Line Items]
Property and equipment, net	2,391	2,544
Goodwill	26,277	24,442
Operating Segments [Member]
Reconciliation of operating segment assets to total assets [Abstract]
Total assets	2,182,752	2,180,664
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total liabilities	644,564	640,416
Operating Segments [Member] \| North America [Member]
Reconciliation of operating segment assets to total assets [Abstract]
Total assets	2,141,822	2,138,768
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total liabilities	571,465	564,832
Operating Segments [Member] \| International [Member]
Reconciliation of operating segment assets to total assets [Abstract]
Total assets	40,930	41,896
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total liabilities	73,099	75,584
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	(73,672)	(78,638)
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total liabilities	$ (63,786)	$ (70,280)

EQUITY OFFERING (Details) - USD ($)	1 Months Ended	9 Months Ended
EQUITY OFFERING (Details) - USD ($)	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Proceeds from (Repurchase of) Equity [Abstract]
Equity offering in period, new shares (in shares)	3,450,000
New shares Issued, price per share (in dollars per share)	$ 160.00
Proceeds from equity offering, net of transaction costs	$ 529,360,000	$ 0	$ 529,360,000
Payments for underwriting expense	22,100,000
Payments of equity offering costs	$ 500,000