CoStar (CSGP) 10-Q 24 Oct 13 2013 Q3 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information	9 Months Ended
	Sep. 30, 2013	Oct. 18, 2013
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	30-Sep-13
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q3
Amendment Flag	FALSE
Entity Common Stock, Shares Outstanding		28,756,248

CONDENSED_CONSOLIDATED_STATEME

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Statement [Abstract]
Revenues	$112,301	$96,001	$325,333	$249,853
Cost of revenues	31,724	30,882	97,431	83,388
Gross margin	80,577	65,119	227,902	166,465
Operating expenses:
Selling and marketing	23,625	22,010	74,139	57,576
Software development	11,562	9,722	35,152	22,714
General and administrative	21,940	19,617	74,457	59,602
Purchase amortization	3,680	4,824	11,699	9,038
Total operating expenses	60,807	56,173	195,447	148,930
Income from operations	19,770	8,946	32,455	17,535
Interest and other income	52	59	239	440
Interest and other expense	-1,736	-1,822	-5,249	-3,022
Income before income taxes	18,086	7,183	27,445	14,953
Income tax expense, net	7,034	404	10,510	9,752
Net income	$11,052	$6,779	$16,935	$5,201
Net income per share-basic (in dollars per share)	$0.40	$0.25	$0.61	$0.20
Net income per share-diluted (in dollars per share)	$0.39	$0.24	$0.60	$0.19
Weighted average outstanding shares-basic (in shares)	27,758	27,243	27,607	26,279
Weighted average outstanding shares-diluted (in shares)	28,349	27,673	28,137	26,691

CONDENSED_CONSOLIDATED_STATEME1

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net income	$11,052	$6,779	$16,935	$5,201
Other comprehensive income, net of tax
Foreign currency translation adjustment	1,652	1,014	20	1,286
Net change in unrealized gain on investments, net of tax	0	727	63	672
Total other comprehensive income	1,652	1,741	83	1,958
Total comprehensive income	$12,704	$8,520	$17,018	$7,159

CONDENSED_CONSOLIDATED_BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$222,938	$156,027
Short-term investments	0	37
Accounts receivable, less allowance for doubtful accounts of approximately $3,646 and $2,935 as of September 30, 2013 and December 31, 2012, respectively	22,960	16,392
Deferred income taxes, net	17,115	9,256
Income tax receivable	1,796	5,357
Prepaid expenses and other current assets	10,021	9,560
Debt issuance costs, net	2,740	2,934
Total current assets	277,570	199,563
Long-term investments	21,675	21,662
Property and equipment, net	55,703	46,308
Goodwill	718,039	718,078
Intangibles and other assets, net	150,800	170,632
Deposits and other assets	2,044	2,274
Debt issuance costs, net	4,543	6,622
Total assets	1,230,374	1,165,139
Current liabilities:
Current portion of long-term debt	21,875	17,500
Accounts payable	6,347	6,234
Accrued wages and commissions	18,256	23,831
Accrued expenses	23,498	19,002
Deferred gain on the sale of building	2,523	2,523
Deferred revenue	34,904	32,548
Total current liabilities	107,403	101,638
Long-term debt, less current portion	135,625	153,125
Deferred gain on the sale of building	26,917	28,809
Deferred rent	22,713	17,305
Deferred income taxes, net	35,482	34,071
Income taxes payable	2,915	2,818
Other long-term liabilities	0	1,030
Total liabilities	331,055	338,796
Stockholders' equity:
Total stockholders’ equity	899,319	826,343
Total liabilities and stockholders’ equity	$1,230,374	$1,165,139

CONDENSED_CONSOLIDATED_BALANCE1

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Current assets:
Allowance for doubtful accounts	$3,646	$2,935

CONDENSED_CONSOLIDATED_STATEME2

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Operating activities:
Net income	$16,935	$5,201
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	9,174	7,203
Amortization	21,063	14,996
Amortization of debt issuance costs	2,273	1,235
Excess tax expense (benefit) from stock-based compensation	-15,405	57
Stock-based compensation expense	32,270	8,667
Deferred income tax expense (benefit), net	-6,448	11,828
Provision for losses on accounts receivable	1,819	1,418
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable	-8,305	-3,612
Prepaid expenses and other current assets	-533	-1,848
Deposits and other assets	220	1,286
Accounts payable and other liabilities	17,413	4,222
Deferred revenue	2,352	5,905
Net cash provided by operating activities	72,828	56,558
Investing activities:
Proceeds from sale and settlement of investments	87	14,620
Purchases of property and equipment and other assets	-15,331	-9,002
Acquisitions, net of cash acquired	0	-640,929
Net cash used in investing activities	-15,244	-635,311
Financing activities:
Proceeds from long-term debt	0	175,000
Payments of long-term debt	-13,125	-4,375
Payments of debt issuance costs	0	-11,546
Payments of deferred consideration	-1,344	0
Excess tax benefit (expense) from stock-based compensation	15,405	-57
Repurchase of restricted stock to satisfy tax withholding obligations	-7,563	-3,817
Proceeds from exercise of stock options and ESPP	15,846	7,667
Net cash provided by financing activities	9,219	162,872
Effect of foreign currency exchange rates on cash and cash equivalents	108	63
Net increase (decrease) in cash and cash equivalents	66,911	-415,818
Cash and cash equivalents at the beginning of period	156,027	545,280
Cash and cash equivalents at the end of period	$222,938	$129,462

ORGANIZATION

ORGANIZATION	9 Months Ended
	Sep. 30, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]
ORGANIZATION	ORGANIZATION
	CoStar Group, Inc. (the “Company” or “CoStar”) provides information, analytics and marketing 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.”) and parts of the United Kingdom ("U.K.") and France, as well as its complementary online marketplace of commercial real estate listings. The Company operates within two operating segments, U.S. 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	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	Basis of Presentation
	The condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Accounting policies are consistent for each operating segment.
	Interim Financial Statements
	The accompanying unaudited condensed consolidated financial statements of the Company have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information. In the opinion of the Company’s management, the financial statements reflect all adjustments necessary to present fairly the Company’s financial position at September 30, 2013, the results of its operations for the three and nine months ended September 30, 2013 and 2012, its comprehensive income for the three and nine months ended September 30, 2013 and 2012, and its cash flows for the nine months ended September 30, 2013 and 2012. 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, 2012.
	The results of operations for the three and nine months ended September 30, 2013 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. Actual results could differ from those estimates.
	Reclassifications
	Certain previously reported amounts in the condensed consolidated statements of operations and condensed consolidated statements of cash flows have been reclassified to conform to the Company’s current presentation.
	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 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 income (loss). Net gains or losses resulting from foreign currency exchange transactions are included in the condensed consolidated statements of operations. There were no material gains or losses from foreign currency exchange transactions for the three and nine months ended September 30, 2013 and 2012.
	2	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED)
	Accumulated Other Comprehensive Loss
	The components of accumulated other comprehensive loss were as follows (in thousands):
		September 30,			December 31,
		2013			2012
	Foreign currency translation adjustment	$	(4,593	)	$	(4,613	)
	Accumulated net unrealized loss on investments, net of tax	(1,842		)	(1,905		)
	Total accumulated other comprehensive loss	$	(6,435	)	$	(6,518	)
	Net Income Per Share
	Net income per share is computed by dividing net income 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 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 per share (in thousands, except per share data):
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013		2012
	Numerator:
	Net income	$	11,052		$	6,779		$	16,935	$	5,201
	Denominator:
	Denominator for basic net income per share — weighted-average outstanding shares	27,758			27,243			27,607		26,279
	Effect of dilutive securities:
	Stock options and restricted stock	591			430			530		412
	Denominator for diluted net income per share — weighted-average outstanding shares	28,349			27,673			28,137		26,691
	Net income per share — basic	$	0.4		$	0.25		$	0.61	$	0.2
	Net income per share — diluted	$	0.39		$	0.24		$	0.6	$	0.19
	Employee stock options with exercise prices greater than the average market price of the Company’s common stock for the period are excluded from the calculation of diluted net income per share as their inclusion would be anti-dilutive. Additionally, shares of restricted common stock that vest based on Company performance conditions were not included in the computation of basic or diluted earnings per share. Other than the shares of restricted common stock that vest based on Company performance conditions, no other potential common shares were excluded from the calculation of diluted net income for the three and nine months ended September 30, 2013 and 2012.
	Stock-Based Compensation
	Equity instruments issued in exchange for employee services are accounted for using a fair-value based method, and the fair value of such equity instruments is recognized as expense in the condensed consolidated statements of operations.
	2	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED)
	Stock-Based Compensation — (Continued)
	Stock-based compensation expense is measured at the grant date of the stock-based awards that vest over set time periods based on their fair values, and is recognized on a straight line basis as expense over the vesting periods of the awards, net of an estimated forfeiture rate. For equity instruments that vest based on performance, the Company assesses the probability of the achievement of the performance conditions at the end of each reporting period, or more frequently based upon the occurrence of events that may change the probability of whether the performance conditions would be met. If the Company's initial estimates of the achievement of the performance conditions change, the related stock-based compensation expense and timing of recognition may fluctuate from period to period based on those estimates. 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.
	In 2012, the Company granted performance-based restricted common stock awards that vest upon the Company's achievement of $90.0 million of cumulative net income before interest, income taxes, depreciation and amortization ("EBITDA") over a period of four consecutive calendar quarters if such performance is achieved by March 31, 2017. As of September 30, 2013, the Company reassessed the probability of achieving this performance condition and determined that it was still probable that the performance condition for these awards would be met by the March 31, 2017 forfeiture date. As a result, the Company recorded a total of approximately $3.1 million and $0 of stock-based compensation expense related to the performance-based restricted common stock for the three months ended September 30, 2013 and 2012, respectively. The Company recorded approximately $17.5 million and $0 of stock-based compensation expense related to the performance-based restricted common stock for the nine months ended September 30, 2013 and 2012, respectively. The Company expects to record an additional estimated unrecognized stock-based compensation expense related to the performance-based restricted common stock of approximately $6.2 million during the remainder of 2013 and in 2014.
	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 related to stock-based compensation in excess of the associated deferred tax asset for such equity compensation. Net cash proceeds from the exercise of stock options and the purchase of shares under the Employee Stock Purchase Plan (“ESPP”) were approximately $6.9 million and $2.6 million for the three months ended September 30, 2013 and 2012, respectively. Net cash proceeds from the exercise of stock options and the purchase of shares under the ESPP were approximately $15.8 million and $7.7 million for the nine months ended September 30, 2013 and 2012, respectively. The Company recorded an increase of approximately $5.7 million of excess tax benefits realized from stock options exercised and restricted stock awards vested for the three months ended September 30, 2013 compared to a reduction of approximately $57,000 to its realized excess tax benefit from stock options exercised and restricted stock awards vested for the three months ended September 30, 2012. The Company recorded an increase of approximately $15.4 million of excess tax benefits realized from stock options exercised and restricted stock awards vested for the nine months ended September 30, 2013 compared to a reduction of approximately $57,000 to its realized excess tax benefit from stock options exercised and restricted stock awards vested for the nine months ended September 30, 2012.
	Stock-based compensation expense for stock options and restricted stock issued under equity incentive plans and stock purchases under the ESPP included in the Company’s results of operations were as follows (in thousands):
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013		2012
	Cost of revenues	$	1,061		$	849		$	3,353	$	1,784
	Selling and marketing	944			493			3,763		1,331
	Software development	1,608			809			5,439		1,565
	General and administrative	4,175			1,588			19,715		3,987
	Total stock-based compensation	$	7,788		$	3,739		$	32,270	$	8,667
	Options to purchase 150,560 and 76,542 shares were exercised during the three months ended September 30, 2013 and 2012, respectively. Options to purchase 340,599 and 224,382 shares were exercised during the nine months ended September 30, 2013 and 2012, respectively.
	2	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED)
	Capitalized Product Development Costs
	Product development costs are expensed as incurred until technological feasibility has been established, at which time such costs are capitalized. Costs are capitalized, to the extent that the capitalizable costs do not exceed the realizable value of such costs, until the product is available for general release to customers. The Company defines the establishment of technological feasibility as the completion of all planning, designing, coding and testing activities that are necessary to establish products that meet design specifications including functions, features and technical performance requirements. The Company's capitalized product development costs had a total net book value of approximately $159,000 and $302,000 as of September 30, 2013 and December 31, 2012, respectively. These capitalized product development costs are included in intangible and other assets in the Company’s condensed consolidated balance sheets. Amortization is computed using a straight-line method over the remaining estimated economic life of the product, typically three to five years after the software is ready for its intended use. The Company amortized capitalized product development costs of approximately $48,000 for each of the three months ended September 30, 2013 and 2012. The Company amortized capitalized product development costs of approximately $143,000 for each of the nine months ended September 30, 2013 and 2012.
	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. The Company had capitalized debt issuance costs of approximately $7.3 million and $9.6 million as of September 30, 2013 and December 31, 2012, 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 and the subsequent term loan facility and revolving credit facility established under a credit agreement dated February 16, 2012 (the “Credit Agreement”). See Note 8 for additional information regarding the financing commitment with J.P. Morgan Bank and the Credit Agreement. The Company amortized debt issuance costs of approximately $760,000 and $763,000 for the three months ended September 30, 2013 and 2012, respectively. The Company amortized debt issuance costs of approximately $2.3 million and $1.2 million for the nine months ended September 30, 2013 and 2012, 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, 2012, including the expected dates of adoption and estimated effects on the Company’s condensed consolidated financial statements, except for the following:
	In July 2012, the Financial Accounting Standards Board (“FASB”) issued authoritative guidance to simplify how companies test indefinite-lived intangible assets for impairment. The guidance permits a company to first assess qualitative factors to determine whether it is more likely than not that an indefinite-lived intangible asset is impaired as a basis for determining whether it is necessary to perform the quantitative impairment test. This guidance is effective for annual and interim impairment tests performed for fiscal years beginning after September 15, 2012, with early adoption permitted. This guidance did not have a material impact on the Company's results of operations or financial position.
	In February 2013, the FASB issued authoritative guidance to improve the reporting of reclassifications out of accumulated other comprehensive income. This guidance requires a company to present, either on the consolidated statements of operations or in the notes to the consolidated financial statements, significant amounts reclassified out of accumulated other comprehensive income by the respective line items of net income, but only if the amount reclassified is required under GAAP to be reclassified in its entirety to net income. For other amounts that are not required under GAAP to be reclassified in their entirety to net income in the same reporting period, an entity is required to cross-reference other disclosures required under GAAP that provide additional detail about those amounts. This guidance is effective prospectively for financial statements issued for interim and annual periods beginning after December 15, 2012. This guidance did not have a material impact on the Company's results of operations or financial position.

ACQUISITIONS

ACQUISITIONS	9 Months Ended
	Sep. 30, 2013
Business Combinations [Abstract]
ACQUISITIONS	ACQUISITIONS
	On April 30, 2012, the Company acquired 100% of the outstanding stock of LoopNet, Inc. (“LoopNet”) pursuant to an Agreement and Plan of Merger dated April 27, 2011, as amended May 20, 2011 (the “Merger Agreement”). LoopNet owns and operates an online marketplace for commercial real estate in the U.S. The online marketplace enables commercial real estate agents, working on behalf of property owners and landlords, to list properties for sale or for lease and submit detailed information on property listings to find a buyer or tenant. The acquisition combines the research capabilities of the Company with the marketing solutions offered by LoopNet to create expected efficiencies in operations and provide more opportunities for the combined company's customers.
	The following table summarizes the consideration paid for LoopNet (in thousands except share and per share data):
	Cash	$	746,393
	Equity interest (1,880,300 shares at $72.89)	137,055
	Fair value of total consideration transferred	$	883,448
	The Company has applied the acquisition method to account for the LoopNet transaction, which requires that, among other things, assets acquired and liabilities assumed be recorded at their fair values as of the acquisition date. The following table summarizes the amounts for acquired assets and liabilities recorded at their fair values as of the acquisition date (in thousands):
	Cash and cash equivalents	$	105,464
	Accounts receivable	3,021
	Goodwill	625,174
	Acquired trade names and other	48,700
	Acquired customer base	71,500
	Acquired database technology	52,100
	Deferred income taxes, net	(32,623		)
	Other assets and liabilities	10,112
	Fair value of identifiable net assets acquired	$	883,448
	The net assets of LoopNet were recorded at their estimated fair value. In valuing acquired assets and liabilities, fair value estimates are based on, but are not limited to, future expected cash flows, expected holding period of investments, 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 10 years. The acquired database technology has an estimated useful life of 5 years and the acquired trade names have an indefinite estimated useful life. 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 is recognized on a straight-line basis over the estimated useful life. The acquired trade names recorded in connection with this acquisition are not amortized, but are subject to annual impairment tests.
	Goodwill recorded in connection with this acquisition is not amortized, but is subject to annual impairment tests. The $625.2 million of goodwill recorded as part of the acquisition is associated with the Company's U.S. operating segment. None of the goodwill recognized is deductible for income tax purposes.
	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 LoopNet acquisition includes: (i) the expected synergies and other benefits that the Company believes will result from combining its operations with LoopNet's operations; and (ii) any intangible assets that do not qualify for separate recognition, such as the assembled workforce.
	There were no acquisition-related costs recorded during the three and nine months ended September 30, 2013. There were no acquisition-related costs recorded during the three months ended September 30, 2012 associated with the LoopNet acquisition. The Company recorded $5.2 million in acquisition-related costs for the nine months ended September 30, 2012. These costs were directly related to acquiring LoopNet and were expensed as incurred and recorded in general and administrative expense.
	3	ACQUISITIONS — (CONTINUED)
	Prior to completion of the LoopNet acquisition, on April 26, 2012, the Federal Trade Commission (the “FTC”) accepted a consent order in connection with the LoopNet merger that was previously agreed to by the Company and LoopNet. The consent order was subject to a 30-day public comment period, and on August 29, 2012, the FTC issued its final acceptance of the consent order. The consent order, which is publicly available on the FTC's website at www.ftc.gov, required, among other things, that the Company and LoopNet divest LoopNet's minority interest in Xceligent, Inc. (“Xceligent”). On March 28, 2012, the Company and LoopNet entered into an agreement to sell LoopNet's interest in Xceligent to DMG Information, Inc. (“DMGI”). The parties closed the sale of LoopNet's interest in Xceligent to DMGI on May 3, 2012. The Company received $4.2 million in proceeds from the sale, which reflected the fair value of the investment at the time of sale and resulted in no gain on the sale of the investment.

INVESTMENTS

INVESTMENTS	9 Months Ended
	Sep. 30, 2013
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. Short-term investments consist of government/federal notes and bonds with maturities greater than 90 days at the time of purchase. Available-for-sale short-term investments with contractual maturities beyond one year are classified as current in the Company’s condensed consolidated balance sheets because they represent the investment of cash that is available for current operations. Long-term investments consist of variable rate debt instruments with an auction reset feature, referred to as auction rate securities (“ARS”). Investments are carried at fair market value.
	Scheduled maturities of investments classified as available-for-sale as of September 30, 2013 were as follows (in thousands):
	Maturity		Fair Value
	Due:
	October 1, 2013 — September 30, 2014		$	—
	October 1, 2014 — September 30, 2018		606
	October 1, 2018 — September 30, 2023		—
	After September 30, 2023		21,069
	Available-for-sale investments		$	21,675
	The Company had no realized gains on its investments for each of the three and nine months ended September 30, 2013 and 2012. The Company had no realized losses on its investments for each of the three and nine months ended September 30, 2013 and 2012.
	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 income (loss) in stockholders’ equity until realized. Realized gains and losses from the sale of available-for-sale securities are determined on a specific-identification basis. A decline in market value of any available-for-sale security below cost that is deemed to be other-than-temporary results in a reduction in carrying amount to fair value. The impairment is charged to earnings and a new cost basis for the security is established. Dividend and interest income are recognized when earned.
	As of September 30, 2013, 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	$	23,517		$	164		$	(2,006	)	$	21,675
	Available-for-sale investments	$	23,517		$	164		$	(2,006	)	$	21,675
	4	INVESTMENTS — (CONTINUED)
	As of December 31, 2012, 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
	Government-sponsored enterprise obligations	$	37		$	—		$	—		$	37
	Auction rate securities	23,567			101			(2,006		)	21,662
	Available-for-sale investments	$	23,604		$	101		$	(2,006	)	$	21,699
	The unrealized losses on the Company’s investments as of September 30, 2013 and December 31, 2012 were generated primarily from changes in interest rates. 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 more likely than not that the Company will not be required to sell these instruments prior to anticipated recovery, which may be at maturity, the Company does not consider these investments to be other-than-temporarily impaired as of September 30, 2013 and December 31, 2012. See Note 5 for further discussion of the fair value of the Company’s financial assets.
	The components of the Company’s investments in an unrealized loss position for twelve months or longer were as follows (in thousands):
		September 30,						December 31,
		2013						2012
		Aggregate			Gross			Aggregate			Gross
		Fair			Unrealized			Fair			Unrealized
		Value			Losses			Value			Losses
	Government-sponsored enterprise obligations	$	—		$	—		$	37		$	—
	Auction rate securities	21,069			(2,006		)	21,119			(2,006		)
	Investments in an unrealized loss position	$	21,069		$	(2,006	)	$	21,156		$	(2,006	)
	The Company did not have any investments in an unrealized loss position for less than twelve months as of September 30, 2013 and December 31, 2012, respectively.

FAIR_VALUE

FAIR VALUE	9 Months Ended
	Sep. 30, 2013
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.
	5	FAIR VALUE — (CONTINUED)
	The following table represents the Company's fair value hierarchy for its financial assets (cash, cash equivalents and investments) and liabilities measured at fair value on a recurring basis as of September 30, 2013 (in thousands):
		Level 1			Level 2			Level 3			Total
	Assets:
	Cash	$	136,909		$	—		$	—		$	136,909
	Money market funds	32,338			—			—			32,338
	Commercial paper	53,691			—			—			53,691
	Auction rate securities	—			—			21,675			21,675
	Total assets measured at fair value	$	222,938		$	—		$	21,675		$	244,613
	Liabilities:
	Deferred consideration	$	—		$	—		$	1,208		$	1,208
	Total liabilities measured at fair value	$	—		$	—		$	1,208		$	1,208
	The following table represents the Company's fair value hierarchy for its financial assets (cash, cash equivalents and investments) and liabilities measured at fair value on a recurring basis as of December 31, 2012 (in thousands):
		Level 1			Level 2			Level 3			Total
	Assets:
	Cash	$	135,232		$	—		$	—		$	135,232
	Money market funds	20,775			—			—			20,775
	Commercial paper	20			—			—			20
	Government-sponsored enterprise obligations	—			37			—			37
	Auction rate securities	—			—			21,662			21,662
	Total assets measured at fair value	$	156,027		$	37		$	21,662		$	177,726
	Liabilities:
	Deferred consideration	$	—		$	—		$	2,304		$	2,304
	Total liabilities measured at fair value	$	—		$	—		$	2,304		$	2,304
	The Company’s Level 2 assets consisted of government-sponsored enterprise obligations, which did not have directly observable quoted prices in active markets. The Company’s Level 2 assets were valued using matrix pricing.
	The Company’s Level 3 assets consist of ARS, whose underlying assets are primarily student loan securities supported by guarantees from the Federal Family Education Loan Program (“FFELP”) of the U.S. Department of Education.
	The following tables summarize changes in fair value of the Company’s Level 3 assets for the three and nine months ended September 30, 2013 and 2012 (in thousands):
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013			2012
	Balance at beginning of period	$	21,675		$	24,976		$	21,662		$	24,584
	Auction rate securities upon acquisition	—			—			—			442
	Change in unrealized gain included in accumulated other comprehensive loss	—			735			63			735
	Settlements	—			(4,150		)	(50		)	(4,200		)
	Balance at end of period	$	21,675		$	21,561		$	21,675		$	21,561
	5	FAIR VALUE — (CONTINUED)
	The following table summarizes changes in fair value of the Company’s Level 3 assets from December 31, 2007 to September 30, 2013 (in thousands):
		Auction
		Rate
		Securities
	Balance at December 31, 2007	$	53,975
	Change in unrealized loss included in accumulated other comprehensive loss	(3,710		)
	Settlements	(20,925		)
	Balance at December 31, 2008	29,340
	Change in unrealized gain included in accumulated other comprehensive loss	684
	Settlements	(300		)
	Balance at December 31, 2009	29,724
	Change in unrealized gain included in accumulated other comprehensive loss	40
	Settlements	(575		)
	Balance at December 31, 2010	29,189
	Change in unrealized gain included in accumulated other comprehensive loss	245
	Settlements	(4,850		)
	Balance at December 31, 2011	24,584
	Auction rate securities upon acquisition	442
	Change in unrealized gain included in accumulated other comprehensive loss	836
	Settlements	(4,200		)
	Balance at December 31, 2012	21,662
	Change in unrealized gain included in accumulated other comprehensive loss	63
	Settlements	(50		)
	Balance at September 30, 2013	$	21,675
	ARS are variable rate debt instruments whose interest rates are reset approximately every 28 days. The majority of the underlying securities have contractual maturities greater than twenty years. The ARS are recorded at fair value.
	As of September 30, 2013, the Company held ARS with $24.3 million par value, all of which failed to settle at auction. The majority of these investments are of high credit quality with AAA credit ratings and are primarily student loan securities supported by guarantees from the FFELP of the U.S. Department of Education. The Company may not be able to liquidate and fully recover the carrying value of the ARS in the near term. As a result, these securities are classified as long-term investments in the Company’s condensed consolidated balance sheet as of September 30, 2013.
While the Company continues to earn interest on its ARS investments at the contractual rate, these investments are not currently actively trading and therefore do not currently have a readily determinable market value. The estimated fair value of the ARS no longer approximates par value. The Company used a discounted cash flow model to determine the estimated fair value of its investment in ARS as of September 30, 2013. The assumptions used in preparing the discounted cash flow model include estimates for interest rates, credit spreads, timing and amount of contractual cash flows, liquidity risk premiums, expected holding periods and default risk. The Company updates the discounted cash flow model on a quarterly basis to reflect any changes in the assumptions used in the model and settlements of ARS investments that occurred during the period.
The only significant unobservable input in the discounted cash flow model is the discount rate. The discount rate used represents the Company's estimate of the yield expected by a market participant from the ARS investments. The weighted average discount rate used in the discounted cash flow model as of September 30, 2013 and December 31, 2012 was approximately 5.2% and 5.1%, 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.
5	FAIR VALUE — (CONTINUED)
Based on this assessment of fair value, as of September 30, 2013, the Company determined there was a decline in the fair value of its ARS investments of approximately $1.8 million. 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.
As of September 30, 2013, the Company held Level 3 liabilities for deferred consideration that it acquired as a result of the April 30, 2012 acquisition of LoopNet. The deferred consideration totaled $1.2 million as of September 30, 2013 and included potential deferred cash payments in connection with acquisitions LoopNet completed in 2010 including: (i) potential deferred cash payments due to the sellers of LandsofAmerica.com, LLC ("LandsofAmerica") on March 31, 2014 based on LandsofAmerica's achievement of financial and operational milestones, resulting in undiscounted deferred consideration as of September 30, 2013 of approximately $1.0 million; and (ii) potential deferred cash payments due to the sellers of Reaction Corp. ("Reaction Web") on March 31, 2014 based on Reaction Web's achievement of revenue milestones, resulting in undiscounted deferred consideration as of September 30, 2013 of approximately $344,000. On March 28, 2013, the Company made a payment of $1.0 million to the sellers of LandsofAmerica for the achievement of financial and operational milestones in 2012 and a payment of approximately $344,000 to the sellers of Reaction Web for the achievement of revenue milestones in 2012.
The following tables summarize changes in fair value of the Company’s Level 3 liabilities for the three and nine months ended September 30, 2013 and 2012 (in thousands):
	Three Months Ended						Nine Months Ended
	September 30,						September 30,
	2013			2012			2013			2012
Balance at beginning of period	$	1,146		$	2,072		$	2,304		$	—
Deferred consideration upon acquisition	—			—			—			2,011
Accretion for period	62			113			248			174
Payments made during period	—			—			(1,344		)	—
Balance at end of period	$	1,208		$	2,185		$	1,208		$	2,185
The following table summarizes changes in fair value of the Company’s Level 3 liabilities from December 31, 2011 to September 30, 2013 (in thousands):
	Deferred
	Consideration
Balance at December 31, 2011	$	—
Deferred consideration upon acquisition	2,011
Accretion for 2012	293
Balance at December 31, 2012	2,304
Accretion from January 1, 2013 – September 30, 2013	248
Payments made from January 1, 2013 – September 30, 2013	(1,344		)
Balance at September 30, 2013	$	1,208
The Company used a discounted cash flow model to determine the estimated fair value of its Level 3 liabilities. The assumptions used in preparing the discounted cash flow model include the discount rate and probabilities for completion of financial and operational milestones.
5	FAIR VALUE — (CONTINUED)
The only significant unobservable input in the discounted cash flow model used to determine the estimated fair value of the Company's Level 3 liabilities is the discount rate. The discount rate used represents LoopNet's cost of equity at the time of each acquisition plus a margin for counterparty risk. The weighted average discount rate used as of September 30, 2013 and December 31, 2012 was approximately 23.5%. 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 deferred consideration.
Concentration of Credit Risk and Financial Instruments
The Company performs ongoing credit evaluations of its customers’ financial condition and generally does not require that its customers’ obligations to the Company be secured. The Company maintains reserves for estimated inherent credit losses, and such losses have been within management’s expectations. The large size and widespread nature of the Company’s customer base and the Company’s lack of dependence on any individual customer mitigates the risk of nonpayment of the Company’s accounts receivable. The carrying amount of the accounts receivable approximates the net realizable value. The carrying value of accounts receivable, accounts payable, accrued expenses, and long-term debt approximates fair value.

GOODWILL

GOODWILL	9 Months Ended
	Sep. 30, 2013
Goodwill [Abstract]
GOODWILL	GOODWILL
	The changes in the carrying amount of goodwill by operating segment consist of the following (in thousands):
		United States		International			Total
	Goodwill, December 31, 2011	$	67,465	$	24,319		$	91,784
	Acquisitions	625,174		—			625,174
	Effect of foreign currency translation	—		1,120			1,120
	Goodwill, December 31, 2012	692,639		25,439			718,078
	Effect of foreign currency translation	—		(39		)	(39		)
	Goodwill, September 30, 2013	$	692,639	$	25,400		$	718,039
	The Company recorded goodwill of approximately $625.2 million in connection with the April 30, 2012 acquisition of LoopNet.

INTANGIBLES_AND_OTHER_ASSETS

INTANGIBLES AND OTHER ASSETS	9 Months Ended
	Sep. 30, 2013
Intangibles and Other Assets [Abstract]
INTANGIBLES AND OTHER ASSETS	INTANGIBLES AND OTHER ASSETS
	Intangibles and other assets consist of the following (in thousands, except amortization period data):
		September 30,			December 31,			Weighted-
		2013			2012			Average
								Amortization
								Period (in years)
	Capitalized product development cost	$	2,140		$	2,140		4
	Accumulated amortization	(1,981		)	(1,838		)
	Capitalized product development cost, net	159			302
	Building photography	13,566			12,474			5
	Accumulated amortization	(11,830		)	(11,639		)
	Building photography, net	1,736			835
	Acquired database technology	77,325			77,328			5
	Accumulated amortization	(38,284		)	(29,673		)
	Acquired database technology, net	39,041			47,655
	Acquired customer base	130,662			130,683			10
	Accumulated amortization	(70,968		)	(59,218		)
	Acquired customer base, net	59,694			71,465
	Acquired trade names and other (1)	59,249			59,255			7
	Accumulated amortization	(9,079		)	(8,880		)
	Acquired trade names and other, net	50,170			50,375
	Intangibles and other assets, net	$	150,800		$	170,632
	(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.

LONGTERM_DEBT

LONG-TERM DEBT	9 Months Ended
	Sep. 30, 2013
Long-term Debt, Current and Noncurrent [Abstract]
LONG-TERM DEBT	LONG-TERM DEBT
	On February 16, 2012, the Company entered into a term loan facility and revolving credit facility pursuant to the Credit Agreement dated February 16, 2012, by and among the Company, as borrower, CoStar Realty Information, Inc. ("CoStar Realty"), as co-borrower, J.P. Morgan Bank, as administrative agent, and the other lenders thereto. The Credit Agreement provides for a $175.0 million term loan facility and a $50.0 million revolving credit facility, each with a term of five years. On April 30, 2012, the Company borrowed $175.0 million under the term loan facility and used those proceeds, together with net proceeds from the Company's equity offering conducted in June 2011, to pay a portion of the merger consideration and transaction costs related to the LoopNet merger. The carrying value of the term loan facility approximates fair value and can be estimated through unobservable inputs using an expected present value 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 the origination.
	8	LONG-TERM DEBT — (CONTINUED)
	The revolving credit facility includes a subfacility for swingline loans of up to $5.0 million and up to $10.0 million of the revolving credit facility is available for the issuances of letters of credit. The term loan facility amortizes in quarterly installments in amounts resulting in an annual amortization of 5% during the first year, 10% during the second year, 15% during the third year, 20% during the fourth year and 50% during the fifth year after the closing date. The loans under the 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 a spread of 2.00% per annum, or (ii) at the greatest of (x) the prime rate from time to time announced by J.P. Morgan Bank, (y) the federal funds effective rate plus ½ of 1% and (z) LIBOR for a one-month interest period plus 1.00%, plus a spread of 1.00% per annum. If an event of default occurs under the Credit Agreement, the interest rate on overdue amounts will increase by 2.00% per annum. The obligations under the Credit Agreement are guaranteed by all material subsidiaries of the Company and secured by a lien on substantially all of the assets of the Company and its material subsidiaries, in each case subject to certain exceptions.
	The Credit Agreement requires the Company to maintain a Debt Service Coverage Ratio (as defined in the Credit Agreement) of at least 1.5 to 1.0 and a Total Leverage Ratio (as defined in the Credit Agreement) that does not exceed 2.75 to 1.00 during each of the three months ending September 30, 2013, December 31, 2013, March 31, 2014 and June 30, 2014; and 2.50 to 1.00 thereafter. The Credit Agreement also includes other covenants that were effective as of April 30, 2012, including covenants that, subject to certain exceptions, restrict the ability of the Company and its subsidiaries (i) to incur additional indebtedness, (ii) to create, incur, assume or permit to exist any liens, (iii) to enter into mergers, consolidations or similar transactions, (iv) to make investments and acquisitions, (v) to make certain dispositions of assets, (vi) to make dividends, distributions and prepayments of certain indebtedness, and (vii) to enter into certain transactions with affiliates. The Company was in compliance with the covenants in the Credit Agreement as of September 30, 2013.
	Commencing with the fiscal year ended December 31, 2012, the Credit Agreement requires the Company to make an annual prepayment of the term loan facility equal to a percentage of Excess Cash Flow (as defined in the Credit Agreement) to reduce the principal amount outstanding under the term loan facility. The prepayment percentage is 50% when the Total Leverage Ratio exceeds 3.00 to 1.00; 25% when the Total Leverage Ratio is greater than 2.50 to 1.00 but equal to or less than 3.00 to 1.00; and 0% when the Total Leverage Ratio is equal to or less than 2.50 to 1.00. This prepayment requirement is reduced by the amount of prior voluntary prepayments during the respective fiscal year, subject to certain exceptions set forth in the Credit Agreement. The Excess Cash Flow payment, if required, is due within ten business days of the date on which the annual financial statements are delivered or required to be delivered to the lenders pursuant to the Credit Agreement. For the fiscal year ended December 31, 2012, the Company was not required to make an Excess Cash Flow payment.
	In connection with obtaining the facility, the Company incurred approximately $11.5 million in debt issuance costs, which were capitalized and are being amortized as interest expense over the term of the Credit Agreement using the effective interest method. The debt issuance costs are comprised of approximately $9.2 million in underwriting fees and approximately $2.3 million primarily related to legal fees associated with the debt issuance.
	As of September 30, 2013 and December 31, 2012, no amounts were outstanding under the revolving credit facility. Total interest expense for the term loan facility was approximately $1.7 million and $1.8 million for the three months ended September 30, 2013 and 2012, respectively, and $5.2 million and $3.0 million for the nine months ended September 30, 2013 and 2012, respectively. Interest expense included amortized debt issuance costs of approximately $760,000 and $763,000 for the three months ended September 30, 2013 and 2012, respectively, and $2.3 million and $1.2 million for the nine months ended September 30, 2013 and 2012, respectively. Total interest paid for the term loan facility was approximately $1.3 million and $1.1 million for the three months ended September 30, 2013 and 2012, respectively, and $3.3 million and $1.8 million for the nine months ended September 30, 2013 and 2012, respectively.

INCOME_TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 2013
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES
	The income tax provision for the nine months ended September 30, 2013 and 2012 reflects an effective tax rate of approximately 38% and 65%, respectively. The higher effective tax rate for the nine months ended September 30, 2012 was primarily due to costs related to the LoopNet acquisition that reduced income from operations but were not deductible for tax purposes.
	9	INCOME TAXES — (CONTINUED)
	The Company is subject to taxation in the U.S. and various states and foreign jurisdictions. The Company is currently under Internal Revenue Service ("IRS") audit in the U.S. for tax year 2010 and its subsidiary LoopNet is under IRS audit for tax years 2009, 2010, 2011 and the four months ended April 30, 2012. While no formal assessments have been received, the Company believes it has provided adequate reserves related to all matters in the tax periods open to examination. Although the timing of income tax audit resolutions and negotiations with taxing authorities is highly uncertain, the Company does not anticipate a significant change to the total amount of unrecognized income tax benefits within the next 12 months.

COMMITMENTS_AND_CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2013
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 February 16, 2012, the Company entered into the Credit Agreement. The Credit Agreement provides for a $175.0 million term loan facility and a $50.0 million revolving credit facility, each with a term of five years. See Note 8 for additional information regarding the Credit Agreement.
	In May 2011, LoopNet, the Board of Directors of LoopNet (“the LoopNet Board”) and/or the Company were named as defendants in three purported class action lawsuits brought by alleged LoopNet stockholders challenging LoopNet's proposed merger with the Company. The stockholder actions alleged, among other things, that (i) each member of the LoopNet Board breached his fiduciary duties to LoopNet and its stockholders in authorizing the sale of LoopNet to the Company, (ii) the merger does not maximize value to LoopNet stockholders, (iii) LoopNet and the Company have made incomplete or materially misleading disclosures about the proposed transaction and (iv) LoopNet and the Company aided and abetted the breaches of fiduciary duty allegedly committed by the members of the LoopNet Board. The stockholder actions sought class action certification and equitable relief, including an injunction against consummation of the merger. The parties have stipulated to the consolidation of the actions, and to permit the filing of a consolidated complaint. In June 2011, counsel for the parties entered into a memorandum of understanding in which they agreed on the terms of a settlement of this litigation, which could result in a loss to the Company of approximately $200,000. On March 20, 2013, the California Superior Court declined to grant preliminary approval to the proposed settlement and issued an order scheduling a hearing on June 11, 2013 to show good cause why the case should not be dismissed. Shortly before the hearing plaintiffs filed a third supplemental submission in support of their motion for preliminary approval of the proposed settlement, and the Court has rescheduled the show cause hearing for February 11, 2014.
	On January 3, 2012, LoopNet, the Company’s wholly owned subsidiary, was sued by CIVIX-DDI, LLC (“Civix”) in the U.S. District Court for the Eastern District of Virginia for alleged infringement of U.S. Patent Nos. 6,385,622 and 6,415,291. The complaint seeks unspecified damages, attorneys' fees and costs. On February 16, 2012, LoopNet filed an answer to Civix’s complaint and filed counterclaims against Civix seeking, among other things, declaratory relief that the asserted patents are invalid, not infringed, and that Civix committed inequitable conduct during the prosecution and re-examination of the asserted patents. On or about May 14, 2012, Civix filed a motion for leave to amend its complaint against LoopNet in the U.S. District Court for the Eastern District of Virginia seeking to add the Company as a defendant, alleging that the Company's products also infringe Civix's patents. The Company filed a motion opposing Civix's motion, and on June 21, 2012, the district court denied Civix's motion to amend its complaint. On June 21, 2012, the Company filed an action in the U.S. District Court for the Northern District of Illinois seeking a declaratory judgment of non-infringement and invalidity against Civix. On August 14, 2012, the Company amended its complaint against Civix to assert an affirmative claim for breach of contract against Civix for Civix's violation of its license agreement and covenant not to sue with one of the Company's technology licensors. On August 30, 2012, the Eastern District of Virginia transferred Civix's case against LoopNet to the Northern District of Illinois, where both cases are now pending. On October 29, 2012, Civix filed a separate action against LoopNet in the Northern District of Illinois alleging infringement of U.S. Patent No. 8,296,335. That case was later consolidated with Civix's original lawsuit against LoopNet. Civix amended its complaint against the Company on November 8, 2012 to add claims under Patent No. 8,296,335 as well. On November 15, 2012, LoopNet filed an amended answer and counterclaim against Civix, asserting an affirmative claim for breach of contract against Civix for Civix's violation of its license agreement and covenant not to sue with one of LoopNet's technology licensors. The U.S. District Court for the Northern District of Illinois construed the language of the patent on September 23, 2013, and has issued a schedule providing for expert discovery and dispositive motions in this case through April 2014, but no trial date has been set. At this time, the Company cannot predict the outcome of either case involving Civix, but the Company intends to vigorously defend itself against Civix's claims.
	10	COMMITMENTS AND CONTINGENCIES — (CONTINUED)
	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 other than as described above. In addition, other than as described above, 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, other than described above. Legal defense costs are expensed as incurred.

SEGMENT_REPORTING

SEGMENT REPORTING	9 Months Ended
	Sep. 30, 2013
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 the U.S. and International, which includes the U.K. and France. The Company’s subscription-based information services consist primarily of CoStar Suite™ and FOCUS™ 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 U.S. operating segment. FOCUS is the Company's primary service offering in the International operating segment. Additionally, the Company introduced CoStar Suite in the U.K. in the fourth quarter of 2012. 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 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						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013			2012
	Revenues
	United States	$	107,230		$	91,153		$	310,762		$	235,606
	International
	External customers	5,071			4,848			14,571			14,247
	Intersegment revenue	131			388			277			1,154
	Total international revenue	5,202			5,236			14,848			15,401
	Intersegment eliminations	(131		)	(388		)	(277		)	(1,154		)
	Total revenues	$	112,301		$	96,001		$	325,333		$	249,853
	EBITDA
	United States	$	30,855		$	22,688		$	66,609		$	46,302
	International	(1,063		)	(3,047		)	(3,917		)	(6,568		)
	Total EBITDA	$	29,792		$	19,641		$	62,692		$	39,734
	Reconciliation of EBITDA to net income
	EBITDA	$	29,792		$	19,641		$	62,692		$	39,734
	Purchase amortization in cost of revenues	(2,954		)	(3,027		)	(9,007		)	(5,607		)
	Purchase amortization in operating expenses	(3,680		)	(4,824		)	(11,699		)	(9,038		)
	Depreciation and other amortization	(3,388		)	(2,844		)	(9,531		)	(7,554		)
	Interest income	52			59			239			440
	Interest expense	(1,736		)	(1,822		)	(5,249		)	(3,022		)
	Income tax expense, net	(7,034		)	(404		)	(10,510		)	(9,752		)
	Net income	$	11,052		$	6,779		$	16,935		$	5,201
	Intersegment revenue is attributable to services performed for the Company’s wholly owned subsidiary, Property and Portfolio Research, Inc. (“PPR”) by Property and Portfolio Research Ltd., a wholly owned subsidiary of PPR. Intersegment revenue is recorded at an amount the Company believes approximates fair value. U.S. EBITDA includes a corresponding cost for the services performed by Property and Portfolio Research Ltd. for PPR.
	U.S. EBITDA includes an allocation of approximately $300,000 and $0 for the three months ended September 30, 2013 and 2012, respectively. U.S. EBITDA includes an allocation of approximately $600,000 and $0 for the nine months ended September 30, 2013 and 2012, respectively. This allocation represents costs incurred for International employees involved in development activities of the Company's U.S. operating segment.
	International EBITDA includes a corporate allocation of approximately $100,000 and $2.3 million for the three months ended September 30, 2013 and 2012, respectively. International EBITDA includes a corporate allocation of approximately $300,000 and $4.5 million for the nine months ended September 30, 2013 and 2012, respectively. The corporate allocation represents costs incurred for U.S. 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):
		September 30,			December 31,
		2013			2012
	Property and equipment, net
	United States	$	51,781		$	42,480
	International	3,922			3,828
	Total property and equipment, net	$	55,703		$	46,308
	Goodwill
	United States	$	692,639		$	692,639
	International	25,400			25,439
	Total goodwill	$	718,039		$	718,078
	Assets
	United States	$	1,285,779		$	1,215,949
	International	41,963			40,933
	Total operating segment assets	$	1,327,742		$	1,256,882
	Reconciliation of operating segment assets to total assets
	Total operating segment assets	$	1,327,742		$	1,256,882
	Investment in subsidiaries	(18,344		)	(18,344		)
	Intersegment receivables	(79,024		)	(73,399		)
	Total assets	$	1,230,374		$	1,165,139
	Liabilities
	United States	$	326,850		$	335,855
	International	77,209			70,108
	Total operating segment liabilities	$	404,059		$	405,963
	Reconciliation of operating segment liabilities to total liabilities
	Total operating segment liabilities	$	404,059		$	405,963
	Intersegment payables	(73,004		)	(67,167		)
	Total liabilities	$	331,055		$	338,796

SUMMARY_OF_SIGNIFICANT_ACCOUNT1

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
	Sep. 30, 2013
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. Actual results could differ from those estimates.
Reclassifications	Reclassifications
	Certain previously reported amounts in the condensed consolidated statements of operations and condensed consolidated statements of cash flows have been reclassified to conform to the Company’s current presentation.
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 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 income (loss). Net gains or losses resulting from foreign currency exchange transactions are included in the condensed consolidated statements of operations. There were no material gains or losses from foreign currency exchange transactions for the three and nine months ended September 30, 2013 and 2012.
Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss
	The components of accumulated other comprehensive loss were as follows (in thousands):
		September 30,			December 31,
		2013			2012
	Foreign currency translation adjustment	$	(4,593	)	$	(4,613	)
	Accumulated net unrealized loss on investments, net of tax	(1,842		)	(1,905		)
	Total accumulated other comprehensive loss	$	(6,435	)	$	(6,518	)
Net Income Per Share	Net Income Per Share
	Net income per share is computed by dividing net income 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 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-Based Compensation	Stock-Based Compensation
	Equity instruments issued in exchange for employee services are accounted for using a fair-value based method, and the fair value of such equity instruments is recognized as expense in the condensed consolidated statements of operations.
	2	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED)
	Stock-Based Compensation — (Continued)
	Stock-based compensation expense is measured at the grant date of the stock-based awards that vest over set time periods based on their fair values, and is recognized on a straight line basis as expense over the vesting periods of the awards, net of an estimated forfeiture rate. For equity instruments that vest based on performance, the Company assesses the probability of the achievement of the performance conditions at the end of each reporting period, or more frequently based upon the occurrence of events that may change the probability of whether the performance conditions would be met. If the Company's initial estimates of the achievement of the performance conditions change, the related stock-based compensation expense and timing of recognition may fluctuate from period to period based on those estimates. 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.
	In 2012, the Company granted performance-based restricted common stock awards that vest upon the Company's achievement of $90.0 million of cumulative net income before interest, income taxes, depreciation and amortization ("EBITDA") over a period of four consecutive calendar quarters if such performance is achieved by March 31, 2017. As of September 30, 2013, the Company reassessed the probability of achieving this performance condition and determined that it was still probable that the performance condition for these awards would be met by the March 31, 2017 forfeiture date. As a result, the Company recorded a total of approximately $3.1 million and $0 of stock-based compensation expense related to the performance-based restricted common stock for the three months ended September 30, 2013 and 2012, respectively. The Company recorded approximately $17.5 million and $0 of stock-based compensation expense related to the performance-based restricted common stock for the nine months ended September 30, 2013 and 2012, respectively. The Company expects to record an additional estimated unrecognized stock-based compensation expense related to the performance-based restricted common stock of approximately $6.2 million during the remainder of 2013 and in 2014.
	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 related to stock-based compensation in excess of the associated deferred tax asset for such equity compensation.
Capitalized Product Development Costs	Capitalized Product Development Costs
	Product development costs are expensed as incurred until technological feasibility has been established, at which time such costs are capitalized. Costs are capitalized, to the extent that the capitalizable costs do not exceed the realizable value of such costs, until the product is available for general release to customers. The Company defines the establishment of technological feasibility as the completion of all planning, designing, coding and testing activities that are necessary to establish products that meet design specifications including functions, features and technical performance requirements. The Company's capitalized product development costs had a total net book value of approximately $159,000 and $302,000 as of September 30, 2013 and December 31, 2012, respectively. These capitalized product development costs are included in intangible and other assets in the Company’s condensed consolidated balance sheets. Amortization is computed using a straight-line method over the remaining estimated economic life of the product, typically three to five years after the software is ready for its intended use. The Company amortized capitalized product development costs of approximately $48,000 for each of the three months ended September 30, 2013 and 2012. The Company amortized capitalized product development costs of approximately $143,000 for each of the nine months ended September 30, 2013 and 2012.
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. The Company had capitalized debt issuance costs of approximately $7.3 million and $9.6 million as of September 30, 2013 and December 31, 2012, 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 and the subsequent term loan facility and revolving credit facility established under a credit agreement dated February 16, 2012 (the “Credit Agreement”). See Note 8 for additional information regarding the financing commitment with J.P. Morgan Bank and the Credit Agreement. The Company amortized debt issuance costs of approximately $760,000 and $763,000 for the three months ended September 30, 2013 and 2012, respectively. The Company amortized debt issuance costs of approximately $2.3 million and $1.2 million for the nine months ended September 30, 2013 and 2012, respectively.
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, 2012, including the expected dates of adoption and estimated effects on the Company’s condensed consolidated financial statements, except for the following:
	In July 2012, the Financial Accounting Standards Board (“FASB”) issued authoritative guidance to simplify how companies test indefinite-lived intangible assets for impairment. The guidance permits a company to first assess qualitative factors to determine whether it is more likely than not that an indefinite-lived intangible asset is impaired as a basis for determining whether it is necessary to perform the quantitative impairment test. This guidance is effective for annual and interim impairment tests performed for fiscal years beginning after September 15, 2012, with early adoption permitted. This guidance did not have a material impact on the Company's results of operations or financial position.
	In February 2013, the FASB issued authoritative guidance to improve the reporting of reclassifications out of accumulated other comprehensive income. This guidance requires a company to present, either on the consolidated statements of operations or in the notes to the consolidated financial statements, significant amounts reclassified out of accumulated other comprehensive income by the respective line items of net income, but only if the amount reclassified is required under GAAP to be reclassified in its entirety to net income. For other amounts that are not required under GAAP to be reclassified in their entirety to net income in the same reporting period, an entity is required to cross-reference other disclosures required under GAAP that provide additional detail about those amounts. This guidance is effective prospectively for financial statements issued for interim and annual periods beginning after December 15, 2012. This guidance did not have a material impact on the Company's results of operations or financial position.

SUMMARY_OF_SIGNIFICANT_ACCOUNT2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]
Schedule of accumulated other comprehensive loss	The components of accumulated other comprehensive loss were as follows (in thousands):
		September 30,			December 31,
		2013			2012
	Foreign currency translation adjustment	$	(4,593	)	$	(4,613	)
	Accumulated net unrealized loss on investments, net of tax	(1,842		)	(1,905		)
	Total accumulated other comprehensive loss	$	(6,435	)	$	(6,518	)
Calculation of basic and diluted net income per share	The following table sets forth the calculation of basic and diluted net income per share (in thousands, except per share data):
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013		2012
	Numerator:
	Net income	$	11,052		$	6,779		$	16,935	$	5,201
	Denominator:
	Denominator for basic net income per share — weighted-average outstanding shares	27,758			27,243			27,607		26,279
	Effect of dilutive securities:
	Stock options and restricted stock	591			430			530		412
	Denominator for diluted net income per share — weighted-average outstanding shares	28,349			27,673			28,137		26,691
	Net income per share — basic	$	0.4		$	0.25		$	0.61	$	0.2
	Net income per share — diluted	$	0.39		$	0.24		$	0.6	$	0.19
Stock-based compensation expense for stock options and restricted stock	Stock-based compensation expense for stock options and restricted stock issued under equity incentive plans and stock purchases under the ESPP included in the Company’s results of operations were as follows (in thousands):
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013		2012
	Cost of revenues	$	1,061		$	849		$	3,353	$	1,784
	Selling and marketing	944			493			3,763		1,331
	Software development	1,608			809			5,439		1,565
	General and administrative	4,175			1,588			19,715		3,987
	Total stock-based compensation	$	7,788		$	3,739		$	32,270	$	8,667

ACQUISITIONS_Tables

ACQUISITIONS (Tables) (LoopNet [Member])	9 Months Ended
	Sep. 30, 2013
LoopNet [Member]
Business Acquisition [Line Items]
Schedule of consideration paid to acquire business	The following table summarizes the consideration paid for LoopNet (in thousands except share and per share data):
	Cash	$	746,393
	Equity interest (1,880,300 shares at $72.89)	137,055
	Fair value of total consideration transferred	$	883,448
Schedule of assets acquired and liabilities assumed	The following table summarizes the amounts for acquired assets and liabilities recorded at their fair values as of the acquisition date (in thousands):
	Cash and cash equivalents	$	105,464
	Accounts receivable	3,021
	Goodwill	625,174
	Acquired trade names and other	48,700
	Acquired customer base	71,500
	Acquired database technology	52,100
	Deferred income taxes, net	(32,623		)
	Other assets and liabilities	10,112
	Fair value of identifiable net assets acquired	$	883,448

INVESTMENTS_Tables

INVESTMENTS (Tables)	9 Months Ended
	Sep. 30, 2013
Investments, Debt and Equity Securities [Abstract]
Scheduled maturities of investments classified as available-for-sale	Scheduled maturities of investments classified as available-for-sale as of September 30, 2013 were as follows (in thousands):
	Maturity		Fair Value
	Due:
	October 1, 2013 — September 30, 2014		$	—
	October 1, 2014 — September 30, 2018		606
	October 1, 2018 — September 30, 2023		—
	After September 30, 2023		21,069
	Available-for-sale investments		$	21,675
Schedule of available for sale securities reconciliation	As of September 30, 2013, 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	$	23,517		$	164		$	(2,006	)	$	21,675
	Available-for-sale investments	$	23,517		$	164		$	(2,006	)	$	21,675
	4	INVESTMENTS — (CONTINUED)
	As of December 31, 2012, 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
	Government-sponsored enterprise obligations	$	37		$	—		$	—		$	37
	Auction rate securities	23,567			101			(2,006		)	21,662
	Available-for-sale investments	$	23,604		$	101		$	(2,006	)	$	21,699
Schedule of unrealized loss on investments	The components of the Company’s investments in an unrealized loss position for twelve months or longer were as follows (in thousands):
		September 30,						December 31,
		2013						2012
		Aggregate			Gross			Aggregate			Gross
		Fair			Unrealized			Fair			Unrealized
		Value			Losses			Value			Losses
	Government-sponsored enterprise obligations	$	—		$	—		$	37		$	—
	Auction rate securities	21,069			(2,006		)	21,119			(2,006		)
	Investments in an unrealized loss position	$	21,069		$	(2,006	)	$	21,156		$	(2,006	)

FAIR_VALUE_Tables

FAIR VALUE (Tables)	9 Months Ended
	Sep. 30, 2013
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) and liabilities measured at fair value on a recurring basis as of September 30, 2013 (in thousands):
		Level 1			Level 2			Level 3			Total
	Assets:
	Cash	$	136,909		$	—		$	—		$	136,909
	Money market funds	32,338			—			—			32,338
	Commercial paper	53,691			—			—			53,691
	Auction rate securities	—			—			21,675			21,675
	Total assets measured at fair value	$	222,938		$	—		$	21,675		$	244,613
	Liabilities:
	Deferred consideration	$	—		$	—		$	1,208		$	1,208
	Total liabilities measured at fair value	$	—		$	—		$	1,208		$	1,208
	The following table represents the Company's fair value hierarchy for its financial assets (cash, cash equivalents and investments) and liabilities measured at fair value on a recurring basis as of December 31, 2012 (in thousands):
		Level 1			Level 2			Level 3			Total
	Assets:
	Cash	$	135,232		$	—		$	—		$	135,232
	Money market funds	20,775			—			—			20,775
	Commercial paper	20			—			—			20
	Government-sponsored enterprise obligations	—			37			—			37
	Auction rate securities	—			—			21,662			21,662
	Total assets measured at fair value	$	156,027		$	37		$	21,662		$	177,726
	Liabilities:
	Deferred consideration	$	—		$	—		$	2,304		$	2,304
	Total liabilities measured at fair value	$	—		$	—		$	2,304		$	2,304
Summary of changes in the fair value of the company's level 3 assets	The following tables summarize changes in fair value of the Company’s Level 3 assets for the three and nine months ended September 30, 2013 and 2012 (in thousands):
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013			2012
	Balance at beginning of period	$	21,675		$	24,976		$	21,662		$	24,584
	Auction rate securities upon acquisition	—			—			—			442
	Change in unrealized gain included in accumulated other comprehensive loss	—			735			63			735
	Settlements	—			(4,150		)	(50		)	(4,200		)
	Balance at end of period	$	21,675		$	21,561		$	21,675		$	21,561
	5	FAIR VALUE — (CONTINUED)
	The following table summarizes changes in fair value of the Company’s Level 3 assets from December 31, 2007 to September 30, 2013 (in thousands):
		Auction
		Rate
		Securities
	Balance at December 31, 2007	$	53,975
	Change in unrealized loss included in accumulated other comprehensive loss	(3,710		)
	Settlements	(20,925		)
	Balance at December 31, 2008	29,340
	Change in unrealized gain included in accumulated other comprehensive loss	684
	Settlements	(300		)
	Balance at December 31, 2009	29,724
	Change in unrealized gain included in accumulated other comprehensive loss	40
	Settlements	(575		)
	Balance at December 31, 2010	29,189
	Change in unrealized gain included in accumulated other comprehensive loss	245
	Settlements	(4,850		)
	Balance at December 31, 2011	24,584
	Auction rate securities upon acquisition	442
	Change in unrealized gain included in accumulated other comprehensive loss	836
	Settlements	(4,200		)
	Balance at December 31, 2012	21,662
	Change in unrealized gain included in accumulated other comprehensive loss	63
	Settlements	(50		)
	Balance at September 30, 2013	$	21,675
Summary of changes in the fair value of the company's level 3 liabilities	The following tables summarize changes in fair value of the Company’s Level 3 liabilities for the three and nine months ended September 30, 2013 and 2012 (in thousands):
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013			2012
	Balance at beginning of period	$	1,146		$	2,072		$	2,304		$	—
	Deferred consideration upon acquisition	—			—			—			2,011
	Accretion for period	62			113			248			174
	Payments made during period	—			—			(1,344		)	—
	Balance at end of period	$	1,208		$	2,185		$	1,208		$	2,185
	The following table summarizes changes in fair value of the Company’s Level 3 liabilities from December 31, 2011 to September 30, 2013 (in thousands):
		Deferred
		Consideration
	Balance at December 31, 2011	$	—
	Deferred consideration upon acquisition	2,011
	Accretion for 2012	293
	Balance at December 31, 2012	2,304
	Accretion from January 1, 2013 – September 30, 2013	248
	Payments made from January 1, 2013 – September 30, 2013	(1,344		)
	Balance at September 30, 2013	$	1,208

GOODWILL_Tables

GOODWILL (Tables)	9 Months Ended
	Sep. 30, 2013
Goodwill [Abstract]
Schedule of Goodwill	The changes in the carrying amount of goodwill by operating segment consist of the following (in thousands):
		United States		International			Total
	Goodwill, December 31, 2011	$	67,465	$	24,319		$	91,784
	Acquisitions	625,174		—			625,174
	Effect of foreign currency translation	—		1,120			1,120
	Goodwill, December 31, 2012	692,639		25,439			718,078
	Effect of foreign currency translation	—		(39		)	(39		)
	Goodwill, September 30, 2013	$	692,639	$	25,400		$	718,039

INTANGIBLES_AND_OTHER_ASSETS_T

INTANGIBLES AND OTHER ASSETS (Tables)	9 Months Ended
	Sep. 30, 2013
Intangibles and Other Assets [Abstract]
Schedule of acquired finite-lived intangible assets by major class	Intangibles and other assets consist of the following (in thousands, except amortization period data):
		September 30,			December 31,			Weighted-
		2013			2012			Average
								Amortization
								Period (in years)
	Capitalized product development cost	$	2,140		$	2,140		4
	Accumulated amortization	(1,981		)	(1,838		)
	Capitalized product development cost, net	159			302
	Building photography	13,566			12,474			5
	Accumulated amortization	(11,830		)	(11,639		)
	Building photography, net	1,736			835
	Acquired database technology	77,325			77,328			5
	Accumulated amortization	(38,284		)	(29,673		)
	Acquired database technology, net	39,041			47,655
	Acquired customer base	130,662			130,683			10
	Accumulated amortization	(70,968		)	(59,218		)
	Acquired customer base, net	59,694			71,465
	Acquired trade names and other (1)	59,249			59,255			7
	Accumulated amortization	(9,079		)	(8,880		)
	Acquired trade names and other, net	50,170			50,375
	Intangibles and other assets, net	$	150,800		$	170,632
	(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)	9 Months Ended
	Sep. 30, 2013
Segment Reporting [Abstract]
Summarized information by operating segment	Summarized information by operating segment consists of the following (in thousands):
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
		2013			2012			2013			2012
	Revenues
	United States	$	107,230		$	91,153		$	310,762		$	235,606
	International
	External customers	5,071			4,848			14,571			14,247
	Intersegment revenue	131			388			277			1,154
	Total international revenue	5,202			5,236			14,848			15,401
	Intersegment eliminations	(131		)	(388		)	(277		)	(1,154		)
	Total revenues	$	112,301		$	96,001		$	325,333		$	249,853
	EBITDA
	United States	$	30,855		$	22,688		$	66,609		$	46,302
	International	(1,063		)	(3,047		)	(3,917		)	(6,568		)
	Total EBITDA	$	29,792		$	19,641		$	62,692		$	39,734
Reconciliation of EBITDA to net income (loss)
	Reconciliation of EBITDA to net income
	EBITDA	$	29,792		$	19,641		$	62,692		$	39,734
	Purchase amortization in cost of revenues	(2,954		)	(3,027		)	(9,007		)	(5,607		)
	Purchase amortization in operating expenses	(3,680		)	(4,824		)	(11,699		)	(9,038		)
	Depreciation and other amortization	(3,388		)	(2,844		)	(9,531		)	(7,554		)
	Interest income	52			59			239			440
	Interest expense	(1,736		)	(1,822		)	(5,249		)	(3,022		)
	Income tax expense, net	(7,034		)	(404		)	(10,510		)	(9,752		)
	Net income	$	11,052		$	6,779		$	16,935		$	5,201
Summarized information by operating segment, assets and liabilities	Summarized information by operating segment consists of the following (in thousands):
		September 30,			December 31,
		2013			2012
	Property and equipment, net
	United States	$	51,781		$	42,480
	International	3,922			3,828
	Total property and equipment, net	$	55,703		$	46,308
	Goodwill
	United States	$	692,639		$	692,639
	International	25,400			25,439
	Total goodwill	$	718,039		$	718,078
	Assets
	United States	$	1,285,779		$	1,215,949
	International	41,963			40,933
	Total operating segment assets	$	1,327,742		$	1,256,882
	Reconciliation of operating segment assets to total assets
	Total operating segment assets	$	1,327,742		$	1,256,882
	Investment in subsidiaries	(18,344		)	(18,344		)
	Intersegment receivables	(79,024		)	(73,399		)
	Total assets	$	1,230,374		$	1,165,139
	Liabilities
	United States	$	326,850		$	335,855
	International	77,209			70,108
	Total operating segment liabilities	$	404,059		$	405,963
	Reconciliation of operating segment liabilities to total liabilities
	Total operating segment liabilities	$	404,059		$	405,963
	Intersegment payables	(73,004		)	(67,167		)
	Total liabilities	$	331,055		$	338,796

ORGANIZATION_Details

ORGANIZATION (Details)	9 Months Ended
	Sep. 30, 2013
	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, NET INCOME (LOSS) PER SHARE (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator: [Abstract]
Net income	$11,052	$6,779	$16,935	$5,201
Denominator: [Abstract]
Denominator for basic net income per share - weighted-average outstanding shares (in shares)	27,758	27,243	27,607	26,279
Effect of dilutive securities: [Abstract]
Stock options and restricted stock	591	430	530	412
Denominator for diluted net income per share - weighted-average outstanding shares (in shares)	28,349	27,673	28,137	26,691
Net income per share - basic (in dollars per share)	$0.40	$0.25	$0.61	$0.20
Net income per share - diluted (in dollars per share)	$0.39	$0.24	$0.60	$0.19
Antidilutive securities excluded from computation of earnings per share	0	0	0	0

SUMMARY_OF_SIGNIFICANT_ACCOUNT4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, ACCUMULATED OTHER COMPREHENSIVE LOSS, NET OF TAX (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Accumulated Other Comprehensive Loss Net of Tax [Abstract]
Foreign currency translation adjustment	($4,593)	($4,613)
Accumulated net unrealzied loss on investments, net of tax	-1,842	-1,905
Total accumulated other comprehensive loss	($6,435)	($6,518)

SUMMARY_OF_SIGNIFICANT_ACCOUNT5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, STOCK BASED COMPENSATION EXPENSE (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Stock-Based Compensation Expense [Abstract]
Compensation expense	$7,788,000	$3,739,000	$32,270,000	$8,667,000
Net cash proceeds from the exercise of stock options and ESPP	6,935,000	2,635,000	15,846,000	7,667,000
Excess tax benefits realized from stock option exercised and restricted stock awards vested	5,655,000	-57,000	15,405,000	-57,000
Exercise of stock options (in shares)	150,560	76,542	340,599	224,382
Cost of Revenues [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	1,061,000	849,000	3,353,000	1,784,000
Selling and Marketing [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	944,000	493,000	3,763,000	1,331,000
Software Development [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	1,608,000	809,000	5,439,000	1,565,000
General and Administrative [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	4,175,000	1,588,000	19,715,000	3,987,000
Performance-Based Restricted Common Stock [Member]
Stock-Based Compensation Expense [Abstract]
Cumulative EBITDA required for award shares to vest	90,000,000		90,000,000
Number of consecutive quarters to mantain cumulative EBITDA required for award shares to vest	4		4
Compensation expense	3,100,000	0	17,500,000	0
Employee service share-based compensation, nonvested awards, total compensation cost not yet recognized	$6,200,000		$6,200,000

SUMMARY_OF_SIGNIFICANT_ACCOUNT6

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, CAPITALIZED PRODUCT DEVELOPMENT AND DEBT ISSUANCE COSTS (Details) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Capitalized Product Development Costs [Abstract]
Capitalized product development costs, net book value	$159		$159		$302
Amortization expense of capitalized product development costs	48	48	143	143
Debt Issuance Cost [Abstract]
Capitalized debt issuance costs	7,283		7,283		9,556
Amortization of debt issuance costs	$760	$763	$2,273	$1,235
Minimum [Member]
Capitalized Product Development Costs [Abstract]
Finite-Lived Intangible Asset, Useful Life			3 years
Maximum [Member]
Capitalized Product Development Costs [Abstract]
Finite-Lived Intangible Asset, Useful Life			5 years

ACQUISITIONS_Details

ACQUISITIONS (Details) (USD $)	Apr. 26, 2012	3-May-12	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Apr. 30, 2012	Sep. 30, 2013	Apr. 30, 2012	Sep. 30, 2013	Apr. 30, 2012
		LoopNet [Member]	LoopNet [Member]	LoopNet [Member]	LoopNet [Member]	LoopNet [Member]	LoopNet [Member]	Acquired Customer Base [Member]	Acquired Customer Base [Member]	Acquired Database Technology [Member]	Acquired Database Technology [Member]
							distinct_intangible_asset		LoopNet [Member]		LoopNet [Member]
Business Acquisition [Line Items]
Percentage of outstanding stock controlled by compnay							100.00%
Distinct intangible asset (in intangible asset)							1
Estimated useful life of acquired assets								10 years	10 years	5 years	5 years
Business combination, recognized goodwill acquired							$625,174,000
Goodwill tax deductible amount							0
Incurred acquisition-related costs			0	0	0	5,200,000
Term of consent order public comment period	30 days
Proceeds from sale of Xcelignet		4,200,000
Gain on sale of Xceligent		$0

ACQUISITIONS_Schedule_of_Consi

ACQUISITIONS (Schedule of Consideration Paid to Aquire LoopNet) (Details) (LoopNet [Member], USD $)	0 Months Ended
In Thousands, except Share data, unless otherwise specified	Apr. 30, 2012
LoopNet [Member]
Business Acquisition [Line Items]
Cash	$746,393
Equity interest, number of shares (in shares)	1,880,300
Equity interest, price per share (in dollars per share)	$72.89
Equity interest	137,055
Fair value of total consideration transferred	$883,448

ACQUISITIONS_Schedule_of_Asset

ACQUISITIONS (Schedule of Assets Acquired and Liabilities Assumed of Loopnet Acquisition) (Details) (LoopNet [Member], USD $)	Apr. 30, 2012
In Thousands, unless otherwise specified
LoopNet [Member]
Business Acquisition [Line Items]
Cash and cash equivalents	$105,464
Accounts receivable	3,021
Goodwill	625,174
Acquired trade names and other	48,700
Acquired customer base	71,500
Acquired database technology	52,100
Deferred income taxes, net	-32,623
Other assets and liabilities	10,112
Fair value of identifiable net assets acquired	$883,448

INVESTMENTS_Details

INVESTMENTS (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, gross realized gains	$0	$0	$0	$0
Available-for-sale securities, gross realized losses	0	0	0	0
Debt Maturities Fair Value [Abstract]
October 1, 2013 — September 30, 2014	0		0
October 1, 2014 — September 30, 2018	606,000		606,000
October 1, 2018 — September 30, 2023	0		0
After September 30, 2023	21,069,000		21,069,000
Fair Value	$21,675,000		$21,675,000		$21,699,000
Minimum [Member]
Investments, Debt and Equity Securities [Abstract]
Short-term investment maturities (in days)			90 days
Available for sale short term investment contractual maturities (in years)			1 year

INVESTMENTS_AVAILABLEFORSALE_S

INVESTMENTS, AVAILABLE-FOR-SALE SECURITIES (Details) (USD $)	9 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$0	$0
Available-for-sale Securities Reconciliation [Abstract]
Amortized Cost	23,517	23,604
Gross Unrealized Gains	164	101
Gross Unrealized Losses	-2,006	-2,006
Fair Value	21,675	21,699
Available-for-sale securities, unrealized loss positions
Aggregate Fair Value	21,069	21,156
Government-Sponsored Enterprise Obligations [Member]
Available-for-sale Securities Reconciliation [Abstract]
Amortized Cost		37
Gross Unrealized Gains		0
Gross Unrealized Losses	0	0
Fair Value		37
Available-for-sale securities, unrealized loss positions
Aggregate Fair Value	0	37
Auction Rate Securities [Member]
Available-for-sale Securities Reconciliation [Abstract]
Amortized Cost	23,517	23,567
Gross Unrealized Gains	164	101
Gross Unrealized Losses	-2,006	-2,006
Fair Value	21,675	21,662
Available-for-sale securities, unrealized loss positions
Aggregate Fair Value	$21,069	$21,119

FAIR_VALUE_Details

FAIR VALUE (Details) (USD $)

3 Months Ended

9 Months Ended

12 Months Ended

9 Months Ended

12 Months Ended

9 Months Ended

12 Months Ended

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2009

Dec. 31, 2008

Sep. 30, 2013

Mar. 28, 2013

Sep. 30, 2013

Mar. 28, 2013

Sep. 30, 2013

Dec. 31, 2012

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Fair Value, Measurements, Recurring [Member]

Auction Rate Securities [Member]

Auction Rate Securities [Member]

Auction Rate Securities [Member]

Auction Rate Securities [Member]

Auction Rate Securities [Member]

Auction Rate Securities [Member]

LandsofAmerica [Member]

LandsofAmerica [Member]

Reaction Web [Member]

Reaction Web [Member]

LoopNet [Member]

LoopNet [Member]

Cash [Member]

Cash [Member]

Money Market Funds [Member]

Money Market Funds [Member]

Commercial Paper [Member]

Commercial Paper [Member]

Government-Sponsored Enterprise Obligations [Member]

Auction Rate Securities [Member]

Auction Rate Securities [Member]

Fair Value, Inputs, Level 1 [Member]

Fair Value, Inputs, Level 1 [Member]

Fair Value, Inputs, Level 1 [Member]

Fair Value, Inputs, Level 1 [Member]

Fair Value, Inputs, Level 1 [Member]

Fair Value, Inputs, Level 1 [Member]

Fair Value, Inputs, Level 1 [Member]

Fair Value, Inputs, Level 1 [Member]

Fair Value, Inputs, Level 1 [Member]

Fair Value, Inputs, Level 1 [Member]

Fair Value, Inputs, Level 1 [Member]

Fair Value, Inputs, Level 2 [Member]

Fair Value, Inputs, Level 2 [Member]

Fair Value, Inputs, Level 2 [Member]

Fair Value, Inputs, Level 2 [Member]

Fair Value, Inputs, Level 2 [Member]

Fair Value, Inputs, Level 2 [Member]

Fair Value, Inputs, Level 2 [Member]

Fair Value, Inputs, Level 2 [Member]

Fair Value, Inputs, Level 2 [Member]

Fair Value, Inputs, Level 2 [Member]

Fair Value, Inputs, Level 2 [Member]

Fair Value, Inputs, Level 3 [Member]

Fair Value, Inputs, Level 3 [Member]

Fair Value, Inputs, Level 3 [Member]

Fair Value, Inputs, Level 3 [Member]

Fair Value, Inputs, Level 3 [Member]

Fair Value, Inputs, Level 3 [Member]

Fair Value, Inputs, Level 3 [Member]

Fair Value, Inputs, Level 3 [Member]

Fair Value, Inputs, Level 3 [Member]

Fair Value, Inputs, Level 3 [Member]

Fair Value, Inputs, Level 3 [Member]

Cash [Member]

Cash [Member]

Money Market Funds [Member]

Money Market Funds [Member]

Commercial Paper [Member]

Commercial Paper [Member]

Government-Sponsored Enterprise Obligations [Member]

Auction Rate Securities [Member]

Auction Rate Securities [Member]

Cash [Member]

Cash [Member]

Money Market Funds [Member]

Money Market Funds [Member]

Commercial Paper [Member]

Commercial Paper [Member]

Government-Sponsored Enterprise Obligations [Member]

Auction Rate Securities [Member]

Auction Rate Securities [Member]

Cash [Member]

Cash [Member]

Money Market Funds [Member]

Money Market Funds [Member]

Commercial Paper [Member]

Commercial Paper [Member]

Government-Sponsored Enterprise Obligations [Member]

Auction Rate Securities [Member]

Auction Rate Securities [Member]

Assets:

Total assets measured at fair value

$244,613,000

$177,726,000

$136,909,000

$135,232,000

$32,338,000

$20,775,000

$53,691,000

$20,000

$37,000

$21,675,000

$21,662,000

$222,938,000

$156,027,000

$136,909,000

$135,232,000

$32,338,000

$20,775,000

$53,691,000

$20,000

$0

$0

$0

$0

$37,000

$0

$0

$0

$0

$0

$0

$37,000

$0

$0

$21,675,000

$21,662,000

$0

$0

$0

$0

$0

$0

$0

$21,675,000

$21,662,000

Unobservable inputs assets (level 3) [Roll forward]

Beginning balance

21,675,000

24,976,000

21,662,000

24,584,000

24,584,000

21,662,000

24,584,000

29,189,000

29,724,000

29,340,000

53,975,000

Auction rate securities upon acquisition

0

0

0

442,000

442,000

Change in unrealized gain (loss) included in accumulated other comprehensive loss

0

735,000

63,000

735,000

63,000

836,000

245,000

40,000

684,000

-3,710,000

Settlements

0

-4,150,000

-50,000

-4,200,000

-50,000

-4,200,000

-4,850,000

-575,000

-300,000

-20,925,000

Ending balance

21,675,000

21,561,000

21,675,000

21,561,000

21,662,000

21,675,000

21,662,000

24,584,000

29,189,000

29,724,000

29,340,000

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

24,300,000

24,300,000

Temporary impairment of the auction rates security investments

-1,842,000

-1,842,000

-1,905,000

Liabilities:

Deferred consideration

1,208,000

2,304,000

0

0

0

0

1,208,000

2,304,000

Unobservable inputs liabilities (level 3) [Roll forward]

Beginning balance

1,146,000

2,072,000

2,304,000

0

0

Deferred consideration upon acquisition

0

0

0

2,011,000

2,011,000

Accretion

62,000

113,000

248,000

174,000

293,000

Payments

0

0

-1,344,000

0

Ending balance

1,208,000

2,185,000

1,208,000

2,185,000

2,304,000

Business acquisition deferred consideration potential cash payment (undiscounted)

1,000,000

344,000

Business acquisition deferred consideration cash payment

$1,000,000

$344,000

Discount rate (in percent)

5.20%

5.10%

23.50%

23.50%

GOODWILL_Details

GOODWILL (Details) (USD $)	9 Months Ended	12 Months Ended	0 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Apr. 30, 2012	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013	Dec. 31, 2012
			LoopNet [Member]	United States [Member]	United States [Member]	International [Member]	International [Member]
Goodwill [Line Items]
Goodwill resulting from acquisition			$625,174
Goodwill [Roll Forward]
Goodwill, beginning balance	718,078	91,784		692,639	67,465	25,439	24,319
Acquisitions		625,174			625,174		0
Effect of foreign currency translation	-39	1,120		0	0	-39	1,120
Goodwill, ending balance	$718,039	$718,078		$692,639	$692,639	$25,400	$25,439

INTANGIBLES_AND_OTHER_ASSETS_D

INTANGIBLES AND OTHER ASSETS (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013	Dec. 31, 2012	Apr. 30, 2012	Apr. 30, 2012	Apr. 30, 2012
In Thousands, unless otherwise specified			Capitalized Product Development Costs [Member]	Capitalized Product Development Costs [Member]	Building Photography [Member]	Building Photography [Member]	Acquired Database Technology [Member]	Acquired Database Technology [Member]	Acquired Customer Base [Member]	Acquired Customer Base [Member]	Acquired Trade Names and Other [Member]	Acquired Trade Names and Other [Member]	LoopNet [Member]	LoopNet [Member]	LoopNet [Member]
														Acquired Database Technology [Member]	Acquired Customer Base [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Business acquisition, purchase price allocation, Intangible assets not amortizable													$48,700
Finite-lived intangible assets, gross			2,140	2,140	13,566	12,474	77,325	77,328	130,662	130,683	59,249	59,255
Finite-lived intangible assets, accumulated amortization			-1,981	-1,838	-11,830	-11,639	-38,284	-29,673	-70,968	-59,218	-9,079	-8,880
Finite-lived intangible assets, net	$150,800	$170,632	$159	$302	$1,736	$835	$39,041	$47,655	$59,694	$71,465	$50,170	$50,375
Weighted-average amortization period (in years}			4 years		5 years		5 years		10 years		7 years			5 years	10 years

LONGTERM_DEBT_LONGTERM_DEBT_De

LONG-TERM DEBT LONG-TERM DEBT (Details) (USD $)

0 Months Ended

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

0 Months Ended

0 Months Ended

Feb. 16, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Jun. 30, 2012

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Feb. 16, 2012

Feb. 16, 2012

Feb. 16, 2012

Apr. 30, 2012

Feb. 16, 2012

Feb. 16, 2012

Feb. 16, 2012

Feb. 16, 2012

Feb. 16, 2012

Feb. 16, 2012

New Term Loan [Member]

New Term Loan [Member]

New Term Loan [Member]

New Term Loan [Member]

CoStar Group [Member]

CoStar Group [Member]

CoStar Group [Member]

CoStar Group [Member]

Minimum [Member]

Maximum [Member]

Maximum [Member]

Maximum [Member]

LIBOR [Member]

Federal Funds Rate [Member]

LoopNet [Member]

LoopNet [Member]

LoopNet [Member]

LoopNet [Member]

CoStar Group [Member]

CoStar Group [Member]

Committed Term Loan [Member]

New Revolving Credit Facility [Member]

New Term Loan [Member]

New Term Loan [Member]

Swingline Loan [Member]

Letter of Credit [Member]

Business Acquisition [Line Items]

Debt instrument borrowing capacity

$50,000,000

$175,000,000

Term of loan (in years)

5 years

5 years

Line of credit facility, amount outstanding

0

0

0

175,000,000

Revolving credit sub-facility for swing-line loans and issuances of letters of credit

5,000,000

10,000,000

Annual amortization, first year after closing (in percent)

5.00%

Annual amortization, second year after closing (in percent)

10.00%

Annual amortization, third year after closing (in percent)

15.00%

Annual amortization, fourth year after closing (in percent)

20.00%

Annual amortization, fifth year after closing (in percent)

50.00%

Basis spread on federal funds rate (in percent)

2.00%

0.50%

LIBOR Maturity Period (in months)

1 month

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%

Default interest rate per annum on overdue amounts (in percent)

2.00%

Maximum debt service coverage ratio for two quarters after closing (in percent)

150.00%

Maximum total leverage ratio for fifth through eighth quarters after closing date (in percent)

275.00%

Maximum total leverage ratio after eight fiscal quarters (in percent)

250.00%

Excess Cash Flow Payment Maturity Period Within Issuance of Financial Statements

10 days

First Excess Cash Flow Repayment, Percentage (in percent)

50.00%

First Excess Cash Flow Repayment Requirement (in percent)

300.00%

Second Excess Cash Flow Repayment, Percentage (in percent)

25.00%

Second Excess Cash Flow Repayment Requirement (in percent)

250.00%

300.00%

Third Excess Cash Flow Repayment, Percentage (in percent)

0.00%

Third Excess Cash Flow Repayment Requirement (in percent

250.00%

Unamortized Debt Issuance Expense

11,500,000

Debt issuance underwriting fees

9,200,000

Legal fees associated with the debt issuance

2,300,000

Interest expense, debt

1,736,000

1,822,000

5,249,000

3,000,000

Amortization of debt issuance costs

760,000

763,000

2,273,000

1,235,000

Interest paid

$1,307,000

$1,059,000

$3,339,000

$1,787,000

INCOME_TAXES_Details

INCOME TAXES (Details)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Income Tax Disclosure [Abstract]
Effective income tax rate (in percent)	38.00%	65.00%

COMMITMENTS_AND_CONTINGENCIES_

COMMITMENTS AND CONTINGENCIES (Details) (USD $)	1 Months Ended			0 Months Ended
	31-May-11	Sep. 30, 2013	Jun. 30, 2011	Feb. 16, 2012	Feb. 16, 2012
	class_action_lawsuits	current_litigation_matters		New Term Loan [Member]	New Revolving Credit Facility [Member]
				CoStar Group [Member]	CoStar Group [Member]
				LoopNet [Member]	LoopNet [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity				$175,000,000	$50,000,000
Term of loan (in years)				5 years	5 years
Class action lawsuits brought by alleged LoopNet stockholders (in lawsuits)	3
Memorandum of understanding in which they agreed on the terms of a settlement of litigation			$200,000
Number of minimum of current litigation matters (in claims)		1

SEGMENT_REPORTING_Details

SEGMENT REPORTING (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
			operating_segments
Segment Reporting Information [Line Items]
Number of business segments (in segments)			2
Summarized information by operating segment [Abstract]
Revenues	$112,301,000	$96,001,000	$325,333,000	$249,853,000
Property and equipment, net	55,703,000		55,703,000		46,308,000
Goodwill	718,039,000		718,039,000		718,078,000	91,784,000
Reconciliation of EBITDA to net income (loss) [Abstract]
EBITDA	29,792,000	19,641,000	62,692,000	39,734,000
Purchase amortization in cost of revenues	-2,954,000	-3,027,000	-9,007,000	-5,607,000
Purchase amortization in operating expenses	-3,680,000	-4,824,000	-11,699,000	-9,038,000
Depreciation and other amortization	-3,388,000	-2,844,000	-9,531,000	-7,554,000
Interest income	52,000	59,000	239,000	440,000
Interest expense	-1,736,000	-1,822,000	-5,249,000	-3,022,000
Income tax expense, net	-7,034,000	-404,000	-10,510,000	-9,752,000
Net income	11,052,000	6,779,000	16,935,000	5,201,000
Reconciliation of operating segment assets to total assets [Abstract]
Total operating segment assets	1,327,742,000		1,327,742,000		1,256,882,000
Investment in subsidiaries	-18,344,000		-18,344,000		-18,344,000
Intersegment receivables	-79,024,000		-79,024,000		-73,399,000
Total assets	1,230,374,000		1,230,374,000		1,165,139,000
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total operating segment liabilities	404,059,000		404,059,000		405,963,000
Intersegment payables	-73,004,000		-73,004,000		-67,167,000
Total liabilities	331,055,000		331,055,000		338,796,000
United States [Member]
Segment Reporting Information [Line Items]
U.S. corporate allocation	300,000	0	600,000	0
Summarized information by operating segment [Abstract]
Revenues	107,230,000	91,153,000	310,762,000	235,606,000
Property and equipment, net	51,781,000		51,781,000		42,480,000
Goodwill	692,639,000		692,639,000		692,639,000	67,465,000
Reconciliation of EBITDA to net income (loss) [Abstract]
EBITDA	30,855,000	22,688,000	66,609,000	46,302,000
Reconciliation of operating segment assets to total assets [Abstract]
Total operating segment assets	1,285,779,000		1,285,779,000		1,215,949,000
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total operating segment liabilities	326,850,000		326,850,000		335,855,000
International [Member]
Segment Reporting Information [Line Items]
International corporate allocation	100,000	2,300,000	300,000	4,500,000
Summarized information by operating segment [Abstract]
Revenues	5,202,000	5,236,000	14,848,000	15,401,000
Property and equipment, net	3,922,000		3,922,000		3,828,000
Goodwill	25,400,000		25,400,000		25,439,000	24,319,000
Reconciliation of EBITDA to net income (loss) [Abstract]
EBITDA	-1,063,000	-3,047,000	-3,917,000	-6,568,000
Reconciliation of operating segment assets to total assets [Abstract]
Total operating segment assets	41,963,000		41,963,000		40,933,000
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total operating segment liabilities	77,209,000		77,209,000		70,108,000
External Customers [Member]
Summarized information by operating segment [Abstract]
Revenues	5,071,000	4,848,000	14,571,000	14,247,000
Intersegment Revenue [Member]
Summarized information by operating segment [Abstract]
Revenues	131,000	388,000	277,000	1,154,000
Intersegment Elimination [Member]
Summarized information by operating segment [Abstract]
Revenues	($131,000)	($388,000)	($277,000)	($1,154,000)