CoStar (CSGP) 10-Q 30 Apr 15 2015 Q1 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information	3 Months Ended
	Mar. 31, 2015	Apr. 24, 2015
Document and Entity Information [Abstract]
Entity Registrant Name	COSTAR GROUP INC
Entity Central Index Key	1057352
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Amendment Flag	FALSE
Entity Common Stock, Shares Outstanding		32,409,761

CONDENSED_CONSOLIDATED_STATEME

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Income Statement [Abstract]
Revenues	$159,020	$119,076
Cost of revenues	45,396	33,643
Gross margin	113,624	85,433
Operating expenses:
Selling and marketing	69,478	27,745
Software development	15,148	12,351
General and administrative	25,363	24,897
Purchase amortization	7,142	3,299
Total operating expenses	117,131	68,292
Income (loss) from operations	-3,507	17,141
Interest and other income	294	137
Interest and other expense	-2,343	-1,615
Income (loss) before income taxes	-5,556	15,663
Income tax expense, net	571	5,923
Net income (loss)	($6,127)	$9,740
Net income (loss) per share-basic (in dollars per share)	($0.19)	$0.34
Net income (loss) per share-diluted (in dollars per share)	($0.19)	$0.34
Weighted average outstanding shares-basic (in shares)	31,831	28,273
Weighted average outstanding shares-diluted (in shares)	31,831	28,840

CONDENSED_CONSOLIDATED_STATEME1

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Net income (loss)	($6,127)	$9,740
Other comprehensive income (loss), net of tax
Foreign currency translation adjustment	-1,261	259
Net decrease in unrealized loss on investments	168	178
Total other comprehensive income (loss)	-1,093	437
Total comprehensive income (loss)	($7,220)	$10,177

CONDENSED_CONSOLIDATED_BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$541,771	$527,012
Accounts receivable, net of allowance for doubtful accounts of approximately $5,006 and $4,815 as of March 31, 2015 and December 31, 2014, respectively	45,699	38,694
Deferred and other income taxes, net	25,604	20,007
Income tax receivable	1,027	1,027
Prepaid expenses and other current assets	10,283	9,736
Debt issuance costs, net	3,320	3,335
Total current assets	627,704	599,811
Long-term investments	16,669	17,151
Property and equipment, net	79,123	73,753
Goodwill	1,137,707	1,138,805
Intangible assets, net	226,699	241,622
Deposits and other assets	2,747	2,676
Debt issuance costs, net	9,052	9,864
Total assets	2,099,701	2,083,682
Current liabilities:
Current portion of long-term debt	20,000	20,000
Accounts payable	6,599	8,608
Accrued wages and commissions	18,899	23,155
Accrued expenses	48,551	27,001
Deferred gain on the sale of building	2,523	2,523
Deferred revenue	39,286	38,003
Total current liabilities	135,858	119,290
Long-term debt, less current portion	360,000	365,000
Deferred gain on the sale of building	23,131	23,762
Deferred rent	27,479	27,032
Deferred income taxes, net	33,539	30,349
Income taxes payable	4,736	4,703
Total liabilities	584,743	570,136
Stockholders' equity:
Total stockholders’ equity	1,514,958	1,513,546
Total liabilities and stockholders’ equity	$2,099,701	$2,083,682

CONDENSED_CONSOLIDATED_BALANCE1

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Current assets:
Allowance for doubtful accounts	$5,006	$4,815

CONDENSED_CONSOLIDATED_STATEME2

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Operating activities:
Net income (loss)	($6,127)	$9,740
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation	4,188	3,540
Amortization	13,625	6,311
Amortization of debt issuance costs	827	710
Impairment loss	1,402	1,053
Excess tax benefit from stock-based compensation	-2,095	-23,429
Stock-based compensation expense	7,442	7,879
Deferred income tax benefit, net	3,886	5,090
Provision for losses on accounts receivable	1,558	986
Changes in operating assets and liabilities:
Accounts receivable	-8,640	-12,499
Prepaid expenses and other current assets	-566	-1,509
Deposits and other assets	-83	39
Accounts payable and other liabilities	13,231	-5,991
Deferred revenue	1,521	1,525
Net cash provided by (used in) operating activities	30,169	-6,555
Investing activities:
Proceeds from sale and settlement of investments	650	0
Purchases of property and equipment and other assets	-11,744	-4,149
Net cash used in investing activities	-11,094	-4,149
Financing activities:
Payments of long-term debt	-5,000	-4,375
Payments of deferred consideration	0	-1,344
Excess tax benefit from stock-based compensation	2,095	23,429
Repurchase of restricted stock to satisfy tax withholding obligations	-5,203	-42,555
Proceeds from exercise of stock options and employee stock purchase plan	4,055	3,001
Net cash used in financing activities	-4,053	-21,844
Effect of foreign currency exchange rates on cash and cash equivalents	-263	38
Net increase (decrease) in cash and cash equivalents	14,759	-32,510
Cash and cash equivalents at the beginning of period	527,012	255,953
Cash and cash equivalents at the end of period	$541,771	$223,443

ORGANIZATION

ORGANIZATION	3 Months Ended
	Mar. 31, 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.”), Toronto, Canada and parts of France. The Company provides online marketplaces for commercial real estate listings, 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_ACCOUNT

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	Basis of Presentation
	The condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Accounting policies are consistent for each operating segment.
	Interim Financial Statements
	The accompanying unaudited condensed consolidated financial statements of the Company have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information. In the opinion of the Company’s management, the financial statements reflect all adjustments necessary to present fairly the Company’s financial position at March 31, 2015 and December 31, 2014, the results of its operations for the three months ended March 31, 2015 and 2014, its comprehensive income (loss) for the three months ended March 31, 2015 and 2014, and its cash flows for the three months ended March 31, 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 months ended March 31, 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, which includes e-commerce, television, radio, print and other media advertising, were approximately $34.6 million and $2.6 million for the three months ended March 31, 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 months ended March 31, 2015 and 2014.
	Accumulated Other Comprehensive Loss
	The components of accumulated other comprehensive loss were as follows (in thousands):
		March 31,			December 31,
		2015			2014
	Foreign currency translation adjustment	$	(6,954	)	$	(5,693	)
	Accumulated net unrealized loss on investments, net of tax	(523		)	(691		)
	Total accumulated other comprehensive loss	$	(7,477	)	$	(6,384	)
	There were no amounts reclassified out of accumulated other comprehensive loss to the condensed consolidated statements of operations for the three months ended March 31, 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
		March 31,
		2015			2014
	Numerator:
	Net income (loss)	$	(6,127	)	$	9,740
	Denominator:
	Denominator for basic net income (loss) per share — weighted-average outstanding shares	31,831			28,273
	Effect of dilutive securities:
	Stock options and restricted stock	—			567
	Denominator for diluted net income (loss) per share — weighted-average outstanding shares	31,831			28,840
	Net income (loss) per share — basic	$	(0.19	)	$	0.34
	Net income (loss) per share — diluted	$	(0.19	)	$	0.34
	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 months ended March 31, 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 88,000 shares that were outstanding for the three months ended March 31, 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, approximately 55,000 and 25,000 shares of restricted common stock that vest based on Company performance and service conditions that have not been achieved as of the end of the period are not included in the computation of basic or diluted earnings per share for the three months ended March 31, 2015 and 2014, respectively. Finally, approximately 1,000 shares of restricted common stock units that vest based on Company service conditions that have not been achieved as of the end of the period are not included in the computation of basic or diluted earnings per share for each of the three months ended March 31, 2015 and 2014, respectively.
	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 $4.1 million and $3.0 million for the three months ended March 31, 2015 and 2014, respectively. The Company realized approximately $2.1 million and $23.4 million of excess tax benefits from stock options exercised and restricted stock awards vested for the three months ended March 31, 2015 and 2014, respectively.
	Stock-based compensation expense for stock options and restricted stock issued under equity incentive plans and stock purchases under the ESPP included in the Company’s results of operations were as follows (in thousands):
		Three Months Ended
		March 31,
		2015			2014
	Cost of revenues	$	1,370		$	1,208
	Selling and marketing	982			1,101
	Software development	1,270			1,447
	General and administrative	3,820			4,123
	Total stock-based compensation	$	7,442		$	7,879
	Options to purchase 38,451 and 43,416 shares were exercised during the three months ended March 31, 2015 and 2014, respectively.
	2	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED)
	Debt Issuance Costs
	Costs incurred in connection with the issuance of long-term debt are capitalized and amortized as interest expense over the term of the related debt using the effective interest method. 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 $12.4 million and $13.2 million as of March 31, 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 $827,000 and $710,000 for the three months ended March 31, 2015 and 2014, respectively.
	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 will 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. Unless the FASB delays the effective date of the new standard, this guidance will be effective on a retrospective basis for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. This guidance permits the use of either a full retrospective method or a modified retrospective approach in which it would be applied only to the most current period presented along with a cumulative-effect adjustment at the date of adoption. In April 2015, the FASB proposed a one-year delay in the effective date of the standard to annual reporting periods beginning after December 15, 2017, with an option that would permit companies to adopt the standard as early as the original effective date. Early application prior to the original effective date is not permitted. A final decision on the effective date is expected in 2015. The Company has not yet 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. This guidance is 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. This guidance is 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.

ACQUISITION

ACQUISITION	3 Months Ended
	Mar. 31, 2015
Business Combinations [Abstract]
ACQUISITION	ACQUISITION
	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, the “Apartments.com Business”). Apartments.com is a national online apartment rentals resource for renters, property managers and owners. Apartments.com offers renters a 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 the Apartments.com Business, 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 the Apartments.com Business as of the Closing Date, and CV paid the Company $2.9 million on July 9, 2014.
	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 the estimated useful life. 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: (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.
	3	ACQUISITION — (CONTINUED)
	As a result of the acquisition of the Apartments.com Business, the Company recorded approximately $1.1 million in acquisition-related costs for the three months ended March 31, 2014. The Company did not record any acquisition-related costs for the three months ended March 31, 2015. These costs include expenses directly related to acquiring the Apartments.com Business, are expensed as incurred and are recorded in general and administrative expense.

INVESTMENTS

INVESTMENTS	3 Months Ended
	Mar. 31, 2015
Investments, Debt and Equity Securities [Abstract]
INVESTMENTS	INVESTMENTS
	The Company determines the appropriate classification of debt and equity investments at the time of purchase and re-evaluates such designation as of each balance sheet date. The Company considers all of its investments to be available-for-sale. The Company's investments consist of long-term variable rate debt instruments with an auction reset feature, referred to as auction rate securities (“ARS”). Investments are carried at fair value.
	Scheduled maturities of investments classified as available-for-sale as of March 31, 2015 are as follows (in thousands):
	Maturity		Fair Value
	Due:
	April 1, 2015 — March 31, 2016		$	—
	April 1, 2016 — March 31, 2020		844
	April 1, 2020 — March 31, 2025		—
	After March 31, 2025		15,825
	Available-for-sale investments		$	16,669
	The Company had no realized gains on its investments for each of the three months ended March 31, 2015 and 2014. The Company had no realized losses on its investments for each of the three months ended March 31, 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 March 31, 2015, the amortized cost basis and fair value of investments classified as available-for-sale were as follows (in thousands):
		Amortized			Gross			Gross			Fair
		Cost			Unrealized			Unrealized			Value
					Gains			Losses
	Auction rate securities	$	17,192		$	402		$	(925	)	$	16,669
	Available-for-sale investments	$	17,192		$	402		$	(925	)	$	16,669
	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			Gross			Gross			Fair
		Cost			Unrealized			Unrealized			Value
					Gains			Losses
	Auction rate securities	$	17,842		$	380		$	(1,071	)	$	17,151
	Available-for-sale investments	$	17,842		$	380		$	(1,071	)	$	17,151
	4	INVESTMENTS — (CONTINUED)
	The unrealized losses on the Company’s investments as of March 31, 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 March 31, 2015 and December 31, 2014. See Note 5 for further discussion of the fair value of the Company’s financial assets.
	The components of the Company’s investments in an unrealized loss position for twelve months or longer were as follows (in thousands):
		March 31,						December 31,
		2015						2014
		Aggregate			Gross			Aggregate			Gross
		Fair			Unrealized			Fair			Unrealized
		Value			Losses			Value			Losses
	Auction rate securities	$	15,825		$	(925	)	$	16,329		$	(1,071	)
	Investments in an unrealized loss position	$	15,825		$	(925	)	$	16,329		$	(1,071	)
	The Company did not have any investments in an unrealized loss position for less than twelve months as of March 31, 2015 and December 31, 2014.

FAIR_VALUE

FAIR VALUE	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
FAIR VALUE	FAIR VALUE
	Fair value is defined as the price that would be received in the sale of an asset or paid to transfer a liability in an orderly transaction between market participants. There is a three-tier fair value hierarchy, which categorizes the inputs used in measuring fair value. These tiers include: Level 1, defined as observable inputs such as quoted prices in active markets for identical assets or liabilities; Level 2, defined as inputs other than quoted prices in active markets that are either directly or indirectly observable; and Level 3, defined as unobservable inputs for which little or no market data exists, therefore requiring an entity to develop its own assumptions.
	The following table represents the Company's fair value hierarchy for its financial assets (cash, cash equivalents and investments) measured at fair value on a recurring basis as of March 31, 2015 (in thousands):
		Level 1			Level 2		Level 3		Total
	Assets:
	Cash	$	336,204		$	—	$	—	$	336,204
	Money market funds	155,816			—		—		155,816
	Commercial paper	49,751			—		—		49,751
	Auction rate securities	—			—		16,669		16,669
	Total assets measured at fair value	$	541,771		$	—	$	16,669	$	558,440
	5	FAIR VALUE — (CONTINUED)
	The following table represents the Company's fair value hierarchy for its financial assets (cash, cash equivalents and investments) measured at fair value on a recurring basis as of December 31, 2014 (in thousands):
		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.
	The following tables summarize changes in fair value of the Company’s Level 3 assets for the three months ended March 31, 2015 and 2014 (in thousands):
		Three Months Ended
		March 31,
		2015			2014
	Balance at beginning of period	$	17,151		$	21,990
	Decrease in unrealized loss included in accumulated other comprehensive loss	168			178
	Settlements	(650		)	—
	Balance at end of period	$	16,669		$	22,168
	5	FAIR VALUE — (CONTINUED)
	The following table summarizes changes in fair value of the Company’s Level 3 assets from December 31, 2007 to March 31, 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	168
	Settlements	(650		)
	Balance at March 31, 2015	$	16,669
	ARS are variable rate debt instruments whose interest rates are reset approximately every 28 days. The majority of the underlying securities have contractual maturities greater than twenty years. The ARS are recorded at fair value.
	As of March 31, 2015, the Company held ARS with $18.0 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 March 31, 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 March 31, 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.
	5	FAIR VALUE — (CONTINUED)
	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 March 31, 2015 and December 31, 2014 was approximately 4.0% 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 March 31, 2015, the Company determined there was a net decline in the fair value of its ARS investments of approximately $523,000. The decline was deemed to be a temporary impairment and recorded as an unrealized loss in accumulated other comprehensive loss in stockholders’ equity. In addition, while a majority of the ARS are currently rated AAA, if the issuers are unable to successfully close future auctions and/or their credit ratings deteriorate, the Company may be required to record additional unrealized losses in accumulated other comprehensive loss or an other-than-temporary impairment charge to earnings on these investments.
Concentration of Credit Risk and Financial Instruments
The Company performs ongoing credit evaluations of its customers’ financial condition and generally does not require that its customers’ obligations to the Company be secured. The Company maintains reserves for estimated inherent credit losses, and such losses have been within management’s expectations. The large size and widespread nature of the Company’s customer base and the Company’s lack of dependence on any individual customer mitigates the risk of nonpayment of the Company’s accounts receivable. The carrying amount of the accounts receivable approximates the net realizable value. The carrying value of accounts receivable, accounts payable, accrued expenses, and long-term debt approximates fair value.

GOODWILL

GOODWILL	3 Months Ended
	Mar. 31, 2015
Goodwill [Abstract]
GOODWILL	GOODWILL
	The changes in the carrying amount of goodwill by operating segment consist of the following (in thousands):
		North America		International			Total
	Goodwill, December 31, 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
	Effect of foreign currency translation	—		(1,098		)	(1,098		)
	Goodwill, March 31, 2015	$	1,114,363	$	23,344		$	1,137,707
	The Company recorded goodwill of approximately $421.7 million in connection with the April 1, 2014 acquisition of the Apartments.com Business.

INTANGIBLE_ASSETS

INTANGIBLE ASSETS	3 Months Ended
	Mar. 31, 2015
Intangibles and Other Assets [Abstract]
INTANGIBLE ASSETS	INTANGIBLE ASSETS
	Intangible assets consist of the following (in thousands, except amortization period data):
		March 31,			December 31,			Weighted-
		2015			2014			Average
								Amortization
								Period (in years)
	Capitalized product development cost	$	2,243		$	2,140		4
	Accumulated amortization	(2,146		)	(2,140		)
	Capitalized product development cost, net	97			—
	Building photography	14,900			14,943			5
	Accumulated amortization	(12,795		)	(12,665		)
	Building photography, net	2,105			2,278
	Acquired database technology	77,163			88,739			5
	Accumulated amortization	(54,527		)	(60,498		)
	Acquired database technology, net	22,636			28,241
	Acquired customer base	199,230			199,826			10
	Accumulated amortization	(109,030		)	(102,443		)
	Acquired customer base, net	90,200			97,383
	Acquired trade names and other intangible assets (1)	127,996			128,171			13
	Accumulated amortization	(16,335		)	(14,451		)
	Acquired trade names and other intangible assets, net	111,661			113,720
	Intangible assets, net	$	226,699		$	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 the Apartments.com Business. The Company evaluated the acquired developed technology for impairment during the first quarter of 2015 and determined that the carrying value of the acquired developed 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.

LONGTERM_DEBT

LONG-TERM DEBT	3 Months Ended
	Mar. 31, 2015
Long-term Debt, Current and Noncurrent [Abstract]
LONG-TERM DEBT	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 the Apartments.com Business. 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 March 31, 2015.
	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.
	8	LONG-TERM DEBT — (CONTINUED)
	As of March 31, 2015 and December 31, 2014, no amounts were outstanding under the revolving credit facilities. Total interest expense for the term loan facilities and revolving credit facilities was approximately $2.3 million and $1.6 million for the three months ended March 31, 2015 and 2014, respectively. Interest expense included amortized debt issuance costs of approximately $827,000 and $710,000 for the three months ended March 31, 2015 and 2014, respectively. Total interest paid for the term loan facilities was approximately $1.5 million and $905,000 for the three months ended March 31, 2015 and 2014, respectively.

INCOME_TAXES

INCOME TAXES	3 Months Ended
	Mar. 31, 2015
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES
	The income tax provision for the three months ended March 31, 2015 and 2014 reflects an effective tax rate of approximately (10)% and 38%, respectively. The change in the effective tax rate is primarily due to a change in local tax law that occurred during the first quarter of 2015.

COMMITMENTS_AND_CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 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

SEGMENT REPORTING	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
SEGMENT REPORTING	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 Canada, and International, which includes the U.K. and France. The Company’s subscription-based information services consist primarily of CoStar SuiteTM services. CoStar Suite is sold as a platform of service offerings consisting of CoStar Property Professional®, CoStar COMPS Professional® and CoStar Tenant® and through the Company's mobile application, CoStarGo®. CoStar Suite is the Company’s primary service offering in the North America and International operating segments. CoStar’s and its subsidiaries' subscription-based services consist primarily of similar services offered over the Internet to commercial real estate industry and related professionals. 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.
	11	SEGMENT REPORTING — (CONTINUED)
	Summarized information by operating segment consists of the following (in thousands):
		Three Months Ended
		March 31,
		2015			2014
	Revenues
	North America	$	153,017		$	113,326
	International
	External customers	6,003			5,750
	Intersegment revenue	8			—
	Total International revenue	6,011			5,750
	Intersegment eliminations	(8		)	—
	Total revenues	$	159,020		$	119,076
	EBITDA
	North America	$	13,677		$	26,368
	International	629			624
	Total EBITDA	$	14,306		$	26,992
	The reconciliation of EBITDA to net income (loss) consists of the following (in thousands):
		Three Months Ended
		March 31,
		2015			2014
	EBITDA	$	14,306		$	26,992
	Purchase amortization in cost of revenues	(6,347		)	(2,877		)
	Purchase amortization in operating expenses	(7,142		)	(3,299		)
	Depreciation and other amortization	(4,324		)	(3,675		)
	Interest income	294			137
	Interest expense	(2,343		)	(1,615		)
	Income tax expense, net	(571		)	(5,923		)
	Net income (loss)	$	(6,127	)	$	9,740
	Intersegment revenue recorded during 2015 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 $200,000 and $400,000 for the three months ended March 31, 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 $100,000 for each of the three months ended March 31, 2015 and 2014. This allocation represents costs incurred for North America employees involved in management and expansion activities of the Company’s International operating segment.
	11	SEGMENT REPORTING — (CONTINUED)
	Summarized information by operating segment consists of the following (in thousands):
		March 31,			December 31,
		2015			2014
	Property and equipment, net
	North America	$	76,512		$	71,209
	International	2,611			2,544
	Total property and equipment, net	$	79,123		$	73,753
	Goodwill
	North America	$	1,114,363		$	1,114,363
	International	23,344			24,442
	Total goodwill	$	1,137,707		$	1,138,805
	Assets
	North America	$	2,157,218		$	2,138,768
	International	38,752			41,896
	Total operating segment assets	$	2,195,970		$	2,180,664
	Reconciliation of operating segment assets to total assets
	Total operating segment assets	$	2,195,970		$	2,180,664
	Investment in subsidiaries	(18,344		)	(18,344		)
	Intersegment receivables	(77,925		)	(78,638		)
	Total assets	$	2,099,701		$	2,083,682
	Liabilities
	North America	$	580,751		$	564,832
	International	70,860			75,584
	Total operating segment liabilities	$	651,611		$	640,416
	Reconciliation of operating segment liabilities to total liabilities
	Total operating segment liabilities	$	651,611		$	640,416
	Intersegment payables	(66,868		)	(70,280		)
	Total liabilities	$	584,743		$	570,136

EQUITY_OFFERING

EQUITY OFFERING	3 Months Ended
	Mar. 31, 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 intends 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 in the future, 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.

SUBSEQUENT_EVENT

SUBSEQUENT EVENT	3 Months Ended
	Mar. 31, 2015
Subsequent Events [Abstract]
SUBSEQUENT EVENT	SUBSEQUENT EVENT
	The Company plans to acquire Apartment Finder pursuant to a definitive agreement and plan of merger with Network Communications, Inc. (the “Merger Agreement”), for $170.0 million in cash, subject to post-closing purchase price adjustments. The Merger Agreement was signed on April 27, 2015. The Company expects the acquisition to close within 90 days, subject to the satisfaction of customary closing conditions. Apartment Finder provides lead generation, advertising, and internet marketing solutions to property managers and owners through its main service, ApartmentFinder.com. The Company is not in a position yet to estimate the financial impact the proposed merger will have on its operations.

SUMMARY_OF_SIGNIFICANT_ACCOUNT1

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 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, which includes e-commerce, television, radio, print and other media advertising, were approximately $34.6 million and $2.6 million for the three months ended March 31, 2015 and 2014, respectively.
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. There were no material gains or losses from foreign currency exchange transactions for the three months ended March 31, 2015 and 2014.
Net Income (Loss) Per Share	Net Income (Loss) Per Share
	Net income (loss) per share is computed by dividing net income (loss) by the weighted average number of common shares outstanding during the period on a basic and diluted basis. The Company’s potentially dilutive securities include stock options and restricted stock. Diluted net income (loss) per share considers the impact of potentially dilutive securities except in periods in which there is a net loss, as the inclusion of the potentially dilutive common shares would have an anti-dilutive effect.
	Stock options to purchase approximately 88,000 shares that were outstanding for the three months ended March 31, 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, approximately 55,000 and 25,000 shares of restricted common stock that vest based on Company performance and service conditions that have not been achieved as of the end of the period are not included in the computation of basic or diluted earnings per share for the three months ended March 31, 2015 and 2014, respectively. Finally, approximately 1,000 shares of restricted common stock units that vest based on Company service conditions that have not been achieved as of the end of the period are not included in the computation of basic or diluted earnings per share for each of the three months ended March 31, 2015 and 2014, respectively.
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.
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 will 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. Unless the FASB delays the effective date of the new standard, this guidance will be effective on a retrospective basis for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. This guidance permits the use of either a full retrospective method or a modified retrospective approach in which it would be applied only to the most current period presented along with a cumulative-effect adjustment at the date of adoption. In April 2015, the FASB proposed a one-year delay in the effective date of the standard to annual reporting periods beginning after December 15, 2017, with an option that would permit companies to adopt the standard as early as the original effective date. Early application prior to the original effective date is not permitted. A final decision on the effective date is expected in 2015. The Company has not yet 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. This guidance is 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. This guidance is 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.

ACQUSITION_ACQUISITION_Policie

ACQUSITION ACQUISITION (Policies)	3 Months Ended
	Mar. 31, 2015
Business Combinations [Abstract]
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.

INVESTMENTS_INVESTMENTS_Polici

INVESTMENTS INVESTMENTS (Policies)	3 Months Ended
	Mar. 31, 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.

COMMITMENTS_AND_CONTINGENCIES_

COMMITMENTS AND CONTINGENCIES COMMITMENTS AND CONTINGENCIES (Policies)	3 Months Ended
	Mar. 31, 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_ACCOUNT2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Schedule of accumulated other comprehensive loss	The components of accumulated other comprehensive loss were as follows (in thousands):
		March 31,			December 31,
		2015			2014
	Foreign currency translation adjustment	$	(6,954	)	$	(5,693	)
	Accumulated net unrealized loss on investments, net of tax	(523		)	(691		)
	Total accumulated other comprehensive loss	$	(7,477	)	$	(6,384	)
Calculation of basic and diluted net income 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
		March 31,
		2015			2014
	Numerator:
	Net income (loss)	$	(6,127	)	$	9,740
	Denominator:
	Denominator for basic net income (loss) per share — weighted-average outstanding shares	31,831			28,273
	Effect of dilutive securities:
	Stock options and restricted stock	—			567
	Denominator for diluted net income (loss) per share — weighted-average outstanding shares	31,831			28,840
	Net income (loss) per share — basic	$	(0.19	)	$	0.34
	Net income (loss) per share — diluted	$	(0.19	)	$	0.34
Stock-based compensation expense for stock options and restricted stock	Stock-based compensation expense for stock options and restricted stock issued under equity incentive plans and stock purchases under the ESPP included in the Company’s results of operations were as follows (in thousands):
		Three Months Ended
		March 31,
		2015			2014
	Cost of revenues	$	1,370		$	1,208
	Selling and marketing	982			1,101
	Software development	1,270			1,447
	General and administrative	3,820			4,123
	Total stock-based compensation	$	7,442		$	7,879

ACQUISITION_Tables

ACQUISITION (Tables)	3 Months Ended
	Mar. 31, 2015
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

INVESTMENTS_Tables

INVESTMENTS (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 2015 are as follows (in thousands):
	Maturity		Fair Value
	Due:
	April 1, 2015 — March 31, 2016		$	—
	April 1, 2016 — March 31, 2020		844
	April 1, 2020 — March 31, 2025		—
	After March 31, 2025		15,825
	Available-for-sale investments		$	16,669
Schedule of available for sale securities reconciliation	As of March 31, 2015, the amortized cost basis and fair value of investments classified as available-for-sale were as follows (in thousands):
		Amortized			Gross			Gross			Fair
		Cost			Unrealized			Unrealized			Value
					Gains			Losses
	Auction rate securities	$	17,192		$	402		$	(925	)	$	16,669
	Available-for-sale investments	$	17,192		$	402		$	(925	)	$	16,669
	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			Gross			Gross			Fair
		Cost			Unrealized			Unrealized			Value
					Gains			Losses
	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):
		March 31,						December 31,
		2015						2014
		Aggregate			Gross			Aggregate			Gross
		Fair			Unrealized			Fair			Unrealized
		Value			Losses			Value			Losses
	Auction rate securities	$	15,825		$	(925	)	$	16,329		$	(1,071	)
	Investments in an unrealized loss position	$	15,825		$	(925	)	$	16,329		$	(1,071	)

FAIR_VALUE_Tables

FAIR VALUE (Tables)	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Summary of fair value hierarchy for its financial assets and liabilities measured at fair value on a recurring basis	The following table represents the Company's fair value hierarchy for its financial assets (cash, cash equivalents and investments) measured at fair value on a recurring basis as of March 31, 2015 (in thousands):
		Level 1			Level 2		Level 3		Total
	Assets:
	Cash	$	336,204		$	—	$	—	$	336,204
	Money market funds	155,816			—		—		155,816
	Commercial paper	49,751			—		—		49,751
	Auction rate securities	—			—		16,669		16,669
	Total assets measured at fair value	$	541,771		$	—	$	16,669	$	558,440
	5	FAIR VALUE — (CONTINUED)
	The following table represents the Company's fair value hierarchy for its financial assets (cash, cash equivalents and investments) measured at fair value on a recurring basis as of December 31, 2014 (in thousands):
		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 months ended March 31, 2015 and 2014 (in thousands):
		Three Months Ended
		March 31,
		2015			2014
	Balance at beginning of period	$	17,151		$	21,990
	Decrease in unrealized loss included in accumulated other comprehensive loss	168			178
	Settlements	(650		)	—
	Balance at end of period	$	16,669		$	22,168
	5	FAIR VALUE — (CONTINUED)
	The following table summarizes changes in fair value of the Company’s Level 3 assets from December 31, 2007 to March 31, 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	168
	Settlements	(650		)
	Balance at March 31, 2015	$	16,669

GOODWILL_Tables

GOODWILL (Tables)	3 Months Ended
	Mar. 31, 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
	Effect of foreign currency translation	—		(1,098		)	(1,098		)
	Goodwill, March 31, 2015	$	1,114,363	$	23,344		$	1,137,707

INTANGIBLE_ASSETS_Tables

INTANGIBLE ASSETS (Tables)	3 Months Ended
	Mar. 31, 2015
Intangibles and Other Assets [Abstract]
Schedule of acquired finite-lived intangible assets by major class	Intangible assets consist of the following (in thousands, except amortization period data):
		March 31,			December 31,			Weighted-
		2015			2014			Average
								Amortization
								Period (in years)
	Capitalized product development cost	$	2,243		$	2,140		4
	Accumulated amortization	(2,146		)	(2,140		)
	Capitalized product development cost, net	97			—
	Building photography	14,900			14,943			5
	Accumulated amortization	(12,795		)	(12,665		)
	Building photography, net	2,105			2,278
	Acquired database technology	77,163			88,739			5
	Accumulated amortization	(54,527		)	(60,498		)
	Acquired database technology, net	22,636			28,241
	Acquired customer base	199,230			199,826			10
	Accumulated amortization	(109,030		)	(102,443		)
	Acquired customer base, net	90,200			97,383
	Acquired trade names and other intangible assets (1)	127,996			128,171			13
	Accumulated amortization	(16,335		)	(14,451		)
	Acquired trade names and other intangible assets, net	111,661			113,720
	Intangible assets, net	$	226,699		$	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.

SEGMENT_REPORTING_Tables

SEGMENT REPORTING (Tables)	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Summarized information by operating segment	Summarized information by operating segment consists of the following (in thousands):
		Three Months Ended
		March 31,
		2015			2014
	Revenues
	North America	$	153,017		$	113,326
	International
	External customers	6,003			5,750
	Intersegment revenue	8			—
	Total International revenue	6,011			5,750
	Intersegment eliminations	(8		)	—
	Total revenues	$	159,020		$	119,076
	EBITDA
	North America	$	13,677		$	26,368
	International	629			624
	Total EBITDA	$	14,306		$	26,992
Reconciliation of EBITDA to net income	The reconciliation of EBITDA to net income (loss) consists of the following (in thousands):
		Three Months Ended
		March 31,
		2015			2014
	EBITDA	$	14,306		$	26,992
	Purchase amortization in cost of revenues	(6,347		)	(2,877		)
	Purchase amortization in operating expenses	(7,142		)	(3,299		)
	Depreciation and other amortization	(4,324		)	(3,675		)
	Interest income	294			137
	Interest expense	(2,343		)	(1,615		)
	Income tax expense, net	(571		)	(5,923		)
	Net income (loss)	$	(6,127	)	$	9,740
Summarized information by operating segment, assets and liabilities	Summarized information by operating segment consists of the following (in thousands):
		March 31,			December 31,
		2015			2014
	Property and equipment, net
	North America	$	76,512		$	71,209
	International	2,611			2,544
	Total property and equipment, net	$	79,123		$	73,753
	Goodwill
	North America	$	1,114,363		$	1,114,363
	International	23,344			24,442
	Total goodwill	$	1,137,707		$	1,138,805
	Assets
	North America	$	2,157,218		$	2,138,768
	International	38,752			41,896
	Total operating segment assets	$	2,195,970		$	2,180,664
	Reconciliation of operating segment assets to total assets
	Total operating segment assets	$	2,195,970		$	2,180,664
	Investment in subsidiaries	(18,344		)	(18,344		)
	Intersegment receivables	(77,925		)	(78,638		)
	Total assets	$	2,099,701		$	2,083,682
	Liabilities
	North America	$	580,751		$	564,832
	International	70,860			75,584
	Total operating segment liabilities	$	651,611		$	640,416
	Reconciliation of operating segment liabilities to total liabilities
	Total operating segment liabilities	$	651,611		$	640,416
	Intersegment payables	(66,868		)	(70,280		)
	Total liabilities	$	584,743		$	570,136

ORGANIZATION_Details

ORGANIZATION (Details)	3 Months Ended
	Mar. 31, 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_ACCOUNT3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, ADVERTISING COSTS (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Accounting Policies [Abstract]
Advertising expense	$34.60	$2.60

SUMMARY_OF_SIGNIFICANT_ACCOUNT4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, FOREIGN CURRENCY AND ACCUMULATED OTHER COMPREHENSIVE LOSS, NET OF TAX (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Accounting Policies [Abstract]
Material gains or losses from foreign currency transactions	$0	$0
Accumulated Other Comprehensive Loss Net of Tax [Abstract]
Foreign currency translation adjustment	-6,954		-5,693
Accumulated net unrealized loss on investments, net of tax	-523		-691
Total accumulated other comprehensive loss	-7,477		-6,384
Reclassification out of accumulated other comprehensive loss	$0	$0

SUMMARY_OF_SIGNIFICANT_ACCOUNT5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, NET INCOME (LOSS) PER SHARE (Details) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Numerator: [Abstract]
Net income (loss)	($6,127)	$9,740
Denominator: [Abstract]
Denominator for basic net income (loss) per share - weighted-average outstanding shares (in shares)	31,831,000	28,273,000
Effect of dilutive securities: [Abstract]
Stock options and restricted stock	0	567,000
Denominator for diluted net income (loss) per share - weighted-average outstanding shares (in shares)	31,831,000	28,840,000
Net income (loss) per share - basic (in dollars per share)	($0.19)	$0.34
Net income (loss) per share - diluted (in dollars per share)	($0.19)	$0.34
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share		88,000
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	25,000
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

SUMMARY_OF_SIGNIFICANT_ACCOUNT6

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, STOCK BASED COMPENSATION EXPENSE (Details) (USD $)	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Stock-Based Compensation Expense [Abstract]
Compensation expense	$7,442	$7,879
Net cash proceeds from the exercise of stock options and ESPP	4,055	3,001
Excess tax benefits realized from stock option exercised and restricted stock awards vested	2,095	23,429
Exercise of stock options (in shares)	38,451	43,416
Cost of Revenues [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	1,370	1,208
Selling and Marketing [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	982	1,101
Software Development [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	1,270	1,447
General and Administrative [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	$3,820	$4,123

SUMMARY_OF_SIGNIFICANT_ACCOUNT7

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, DEBT ISSUANCE COSTS (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Apr. 01, 2014
Deferred Finance Costs, Own-share Lending Arrangement, Issuance Costs, Net [Abstract]
Capitalized debt issuance costs	$12,372		$13,199	$10,000
Amortization of debt issuance costs	$827	$710

ACQUISITION_Details

ACQUISITION (Details) (USD $)	0 Months Ended	3 Months Ended
	Apr. 03, 2014	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Apr. 01, 2014
Business Acquisition [Line Items]
Payments to acquire businesses	$587,104,000
Closing purchase price adjustments	2,104,000
Post closing purchase price adjustments	2,886,000
Goodwill		1,137,707,000		1,138,805,000	718,587,000
Apartments.com [Member]
Business Acquisition [Line Items]
Goodwill						421,724,000
Goodwill tax deductible amount						421,724,000
Business combination, acquisition related costs		$0	$1,100,000
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						1
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
Trade Names and Other Intangible Assets [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets		13 years
Trade Names and Other Intangible Assets [Member] | Apartments.com [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets	13 years
Building Photography [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets		5 years
Building Photography [Member] | Apartments.com [Member]
Business Acquisition [Line Items]
Estimated useful life of acquired assets	3 years

ACQUSITION_ACQUISITION_Details

ACQUSITION ACQUISITION (Details - Schedule of Assets Acquired and Liabilities Assumed) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Apr. 01, 2014
In Thousands, unless otherwise specified
Business Acquisition [Line Items]
Goodwill	$1,137,707	$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

INVESTMENTS_SCHEDULED_MATURITI

INVESTMENTS, SCHEDULED MATURITIES AND REALIZED GAINS AND LOSSES (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, gross realized gains	$0	$0
Available-for-sale securities, gross realized losses	0	0
Debt Maturities Fair Value [Abstract]
April 1, 2015 — March 31, 2016	0
April 1, 2016 — March 31, 2020	844,000
April 1, 2020 — March 31, 2025	0
After March 31, 2025	15,825,000
Fair Value	$16,669,000		$17,151,000

INVESTMENTS_AVAILABLEFORSALE_S

INVESTMENTS, AVAILABLE-FOR-SALE SECURITIES (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
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	17,192	17,842
Gross Unrealized Gains	402	380
Gross Unrealized Losses	-925	-1,071
Fair Value	16,669	17,151
Available-for-sale securities, unrealized loss positions
Aggregate Fair Value	15,825	16,329
Auction Rate Securities [Member]
Available-for-sale Securities Reconciliation [Abstract]
Amortized Cost	17,192	17,842
Gross Unrealized Gains	402	380
Gross Unrealized Losses	-925	-1,071
Fair Value	16,669	17,151
Available-for-sale securities, unrealized loss positions
Aggregate Fair Value	$15,825	$16,329

FAIR_VALUE_Details

FAIR VALUE (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 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	$17,151,000	$21,990,000	$21,990,000
Change in unrealized gain (loss) included in accumulated other comprehensive loss	168,000	178,000
Settlements	-650,000	0
Ending balance	16,669,000	22,168,000
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	18,000,000
Temporary impairment of the auction rates security investments, net of unrealized gain	-523,000		-691,000
Fair Value, Measurements, Recurring [Member]
Assets:
Total assets measured at fair value	558,440,000		544,163,000
Fair Value, Measurements, Recurring [Member] | Cash [Member]
Assets:
Total assets measured at fair value	336,204,000		160,275,000
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Assets:
Total assets measured at fair value	155,816,000		310,482,000
Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member]
Assets:
Total assets measured at fair value	49,751,000		56,255,000
Fair Value, Measurements, Recurring [Member] | Auction Rate Securities [Member]
Assets:
Total assets measured at fair value	16,669,000		17,151,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets:
Total assets measured at fair value	541,771,000		527,012,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Cash [Member]
Assets:
Total assets measured at fair value	336,204,000		160,275,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Assets:
Total assets measured at fair value	155,816,000		310,482,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commercial Paper [Member]
Assets:
Total assets measured at fair value	49,751,000		56,255,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Auction Rate Securities [Member]
Assets:
Total assets measured at fair value	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets:
Total assets measured at fair value	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Cash [Member]
Assets:
Total assets measured at fair value	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
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commercial Paper [Member]
Assets:
Total assets measured at fair value	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
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets:
Total assets measured at fair value	16,669,000		17,151,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Cash [Member]
Assets:
Total assets measured at fair value	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
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commercial Paper [Member]
Assets:
Total assets measured at fair value	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Auction Rate Securities [Member]
Assets:
Total assets measured at fair value	16,669,000		17,151,000
Auction Rate Securities [Member]
Unobservable inputs assets (level 3) [Roll forward]
Beginning balance	17,151,000	21,990,000	21,990,000	21,662,000	24,584,000	29,189,000	29,724,000	29,340,000	53,975,000
Change in unrealized gain (loss) included in accumulated other comprehensive loss	168,000		836,000	378,000	836,000	245,000	40,000	684,000	-3,710,000
Settlements	-650,000		-5,675,000	-50,000	-4,200,000	-4,850,000	-575,000	-300,000	-20,925,000
Auction rate securities upon acquisition					442,000
Ending balance	$16,669,000		$17,151,000	$21,990,000	$21,662,000	$24,584,000	$29,189,000	$29,724,000	$29,340,000
Discount rate (in percent)	4.00%		4.10%

GOODWILL_Details

GOODWILL (Details) (USD $)	3 Months Ended	12 Months Ended	0 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Apr. 03, 2014
Goodwill [Roll Forward]
Goodwill, beginning balance	$1,138,805	$718,587
Effect of foreign currency translation	-1,098	-1,506
Acquisition		421,724
Goodwill, ending balance	1,137,707	1,138,805
Apartments.com [Member]
Goodwill [Line Items]
Goodwill, period increase			421,724
Goodwill [Roll Forward]
Goodwill, beginning balance			421,724
North America [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	1,114,363	692,639
Effect of foreign currency translation	0	0
Acquisition		421,724
Goodwill, ending balance	1,114,363	1,114,363
International [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	24,442	25,948
Effect of foreign currency translation	-1,098	-1,506
Acquisition		0
Goodwill, ending balance	$23,344	$24,442

INTANGIBLE_ASSETS_Details

INTANGIBLE ASSETS (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Apr. 30, 2012
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net	$226,699,000		$241,622,000
Impairment of intangible assets, finite-lived	1,402,000	1,053,000
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	-2,146,000		-2,140,000
Finite-lived intangible assets, net	97,000		0
Weighted-average amortization period (in years}	4 years
Building Photography [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	14,900,000		14,943,000
Finite-lived intangible assets, accumulated amortization	-12,795,000		-12,665,000
Finite-lived intangible assets, net	2,105,000		2,278,000
Weighted-average amortization period (in years}	5 years
Developed Technology Rights [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	77,163,000		88,739,000
Finite-lived intangible assets, accumulated amortization	-54,527,000		-60,498,000
Finite-lived intangible assets, net	22,636,000		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	199,230,000		199,826,000
Finite-lived intangible assets, accumulated amortization	-109,030,000		-102,443,000
Finite-lived intangible assets, net	90,200,000		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	127,996,000		128,171,000
Finite-lived intangible assets, accumulated amortization	-16,335,000		-14,451,000
Finite-lived intangible assets, net	111,661,000		113,720,000
Weighted-average amortization period (in years}	13 years
LoopNet [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Business acquisition, purchase price allocation, intangible assets not amortizable				$48,700,000

LONGTERM_DEBT_Details

LONG-TERM DEBT (Details) (USD $)	0 Months Ended	1 Months Ended	3 Months Ended
	Apr. 03, 2014	Jun. 30, 2014	Apr. 04, 2014	Mar. 31, 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				12,372,000	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%

LONGTERM_DEBT_Details_Covenant

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%

LONGTERM_DEBT_Details_Interest

LONG-TERM DEBT (Details - Interest Expense and Amortization of Debt Issuance Costs) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Apr. 01, 2014	Dec. 31, 2014
Debt Instrument [Line Items]
Line of credit facility, amount outstanding			$150,000,000
Interest expense, debt	2,343,000	1,615,000
Amortization of debt issuance costs	827,000	710,000
Interest paid	1,518,000	905,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, amount outstanding	$0			$0

INCOME_TAXES_Details

INCOME TAXES (Details)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Tax Disclosure [Abstract]
Effective income tax rate (in percent)	-10.00%	38.00%

COMMITMENTS_AND_CONTINGENCIES_1

COMMITMENTS AND CONTINGENCIES (Details) (CoStar Group [Member], USD $)	0 Months Ended
In Millions, unless otherwise specified	Apr. 03, 2014	Apr. 01, 2014
Term Loan [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity		$400
Term of loan (in years)	5 years
Revolving Credit Facility [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity		$225
Term of loan (in years)	5 years

SEGMENT_REPORTING_Details

SEGMENT REPORTING (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
	operating_segments
Segment Reporting Information [Line Items]
Number of business segments (in segments)	2
Summarized information by operating segment [Abstract]
Revenues	$159,020,000	$119,076,000
Property and equipment, net	79,123,000		73,753,000
Goodwill	1,137,707,000		1,138,805,000	718,587,000
Reconciliation of EBITDA to net income (loss) [Abstract]
EBITDA	14,306,000	26,992,000
Purchase amortization in cost of revenues	-6,347,000	-2,877,000
Purchase amortization in operating expenses	-7,142,000	-3,299,000
Depreciation and other amortization	-4,324,000	-3,675,000
Interest income	294,000	137,000
Interest expense	-2,343,000	-1,615,000
Income tax expense, net	-571,000	-5,923,000
Net income (loss)	-6,127,000	9,740,000
Reconciliation of operating segment assets to total assets [Abstract]
Total operating segment assets	2,195,970,000		2,180,664,000
Investment in subsidiaries	-18,344,000		-18,344,000
Intersegment receivables	-77,925,000		-78,638,000
Total assets	2,099,701,000		2,083,682,000
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total operating segment liabilities	651,611,000		640,416,000
Intersegment payables	-66,868,000		-70,280,000
Total liabilities	584,743,000		570,136,000
North America [Member]
Segment Reporting Information [Line Items]
North America corporate allocation	200,000	400,000
Summarized information by operating segment [Abstract]
Revenues	153,017,000	113,326,000
Property and equipment, net	76,512,000		71,209,000
Goodwill	1,114,363,000		1,114,363,000	692,639,000
Reconciliation of EBITDA to net income (loss) [Abstract]
EBITDA	13,677,000	26,368,000
Reconciliation of operating segment assets to total assets [Abstract]
Total operating segment assets	2,157,218,000		2,138,768,000
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total operating segment liabilities	580,751,000		564,832,000
International [Member]
Segment Reporting Information [Line Items]
International corporate allocation	100,000	100,000
Summarized information by operating segment [Abstract]
Revenues	6,011,000	5,750,000
Property and equipment, net	2,611,000		2,544,000
Goodwill	23,344,000		24,442,000	25,948,000
Reconciliation of EBITDA to net income (loss) [Abstract]
EBITDA	629,000	624,000
Reconciliation of operating segment assets to total assets [Abstract]
Total operating segment assets	38,752,000		41,896,000
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total operating segment liabilities	70,860,000		75,584,000
External Customers [Member]
Summarized information by operating segment [Abstract]
Revenues	6,003,000	5,750,000
Intersegment Revenue [Member]
Summarized information by operating segment [Abstract]
Revenues	8,000	0
Intersegment Elimination [Member]
Summarized information by operating segment [Abstract]
Revenues	($8,000)	$0

EQUITY_OFFERING_Details

EQUITY OFFERING (Details) (USD $)	1 Months Ended
	Jun. 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
Proceeds from equity offering, net of transaction costs	$529,360,000
Payments for underwriting expense	22,100,000
Payments of equity offering costs	$500,000

SUBSEQUENT_EVENT_Details

SUBSEQUENT EVENT (Details) (USD $)	Mar. 31, 2015
In Millions, unless otherwise specified
Subsequent Events [Abstract]
Proposed business combination consideration	$170