CoStar (CSGP) 10-K 20 Feb 14 2013 FY Annual report Financial data

DOCUMENT_AND_ENTITY_INFORMATIO

DOCUMENT AND ENTITY INFORMATION DOCUMENT AND ENTITY INFORMATION (USD $)	12 Months Ended
In Billions, except Share data, unless otherwise specified	Dec. 31, 2013	Feb. 14, 2014	Jun. 28, 2013
Document and Entity Information [Abstract]	'	'	'
Entity Registrant Name	'COSTAR GROUP INC	'	'
Entity Central Index Key	'0001057352	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Well-known Seasoned Issuer	'Yes	'	'
Entity Voluntary Filers	'No	'	'
Entity Current Reporting Status	'Yes	'	'
Entity Filer Category	'Large Accelerated Filer	'	'
Entity Public Float	'	'	$3.50
Entity Common Stock, Shares Outstanding (in shares)	'	28,853,559	'
Document Fiscal Year Focus	'2013	'	'
Document Fiscal Period Focus	'FY	'	'
Document Type	'10-K	'	'
Amendment Flag	'false	'	'
Document Period End Date	31-Dec-13	'	'

CONSOLIDATED_STATEMENTS_OF_OPE

CONSOLIDATED STATEMENTS OF OPERATIONS (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement [Abstract]	'	'	'
Revenues	$440,943	$349,936	$251,738
Cost of revenues	129,185	114,866	88,167
Gross margin	311,758	235,070	163,571
Operating expenses:	'	'	'
Selling and marketing	98,708	84,113	61,164
Software development	46,757	32,756	20,037
General and administrative	96,956	77,154	58,362
Purchase amortization	15,183	13,607	2,237
Total operating expenses	257,604	207,630	141,800
Income from operations	54,154	27,440	21,771
Interest and other income	326	526	798
Interest and other expense	-6,943	-4,832	0
Income before income taxes	47,537	23,134	22,569
Income tax expense, net	17,803	13,219	7,913
Net income	$29,734	$9,915	$14,656
Net income per share — basic (in dollars per share)	$1.07	$0.37	$0.63
Net income per share — diluted (in dollars per share)	$1.05	$0.37	$0.62
Weighted average outstanding shares — basic (in shares)	27,670	26,533	23,131
Weighted average outstanding shares — diluted (in shares)	28,212	26,949	23,527

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement of Comprehensive Income [Abstract]	'	'	'
Net income	$29,734	$9,915	$14,656
Other comprehensive income, net of tax	'	'	'
Foreign currency translation adjustment	610	1,277	25
Net decrease in unrealized loss on investments	378	773	113
Total other comprehensive income	988	2,050	138
Total comprehensive income	$30,722	$11,965	$14,794

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$255,953	$156,027
Short-term investments	0	37
Accounts receivable, less allowance for doubtful accounts of approximately $2,935 and $3,397 as of December 31, 2012 and 2013, respectively	20,761	16,392
Deferred income taxes, net	22,506	9,256
Income tax receivable	0	5,357
Prepaid expenses and other current assets	6,597	9,560
Debt issuance costs, net	2,649	2,934
Total current assets	308,466	199,563
Long-term investments	21,990	21,662
Property and equipment, net	57,719	46,308
Goodwill	718,587	718,078
Intangibles and other assets, net	144,472	170,632
Deposits and other assets	1,855	2,274
Debt issuance costs, net	3,893	6,622
Total assets	1,256,982	1,165,139
Current liabilities:	'	'
Current portion of long-term debt	24,063	17,500
Accounts payable	4,939	6,234
Accrued wages and commissions	20,104	23,831
Accrued expenses	23,200	19,002
Deferred gain on the sale of building	2,523	2,523
Income taxes payable	2,362	0
Deferred revenue	34,362	32,548
Total current liabilities	111,553	101,638
Long-term debt, less current portion	129,062	153,125
Deferred gain on the sale of building	26,286	28,809
Deferred rent	22,828	17,305
Deferred income taxes, net	34,582	34,071
Income taxes payable	4,809	2,818
Other long-term liabilities	0	1,030
Total liabilities	329,120	338,796
Commitments and contingencies	'	'
Stockholders’ equity:	'	'
Preferred stock, $0.01 par value; 2,000 shares authorized; none outstanding	0	0
Common stock, $0.01 par value; 60,000 shares authorized; 28,348 and 28,848 issued and outstanding as of December 31, 2012 and 2013, respectively	288	283
Additional paid-in capital	863,780	792,988
Accumulated other comprehensive loss	-5,530	-6,518
Retained earnings	69,324	39,590
Total stockholders’ equity	927,862	826,343
Total liabilities and stockholders’ equity	$1,256,982	$1,165,139

CONSOLIDATED_BALANCE_SHEETS_Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, except Share data, unless otherwise specified
Allowance for doubtful accounts	$3,397	$2,935
Preferred stock, par value (in dollars per share)	$0.01	$0.01
Preferred stock, shares authorized (in shares)	2,000,000	2,000,000
Preferred stock, shares outstanding (in shares)	0	0
Common stock par value (in dollars per share)	$0.01	$0.01
Common stock, shares authorized (in shares)	60,000,000	60,000,000
Common stock, shares issued, (in shares)	28,848,000	28,348,000
Common stock, shares outstanding (in shares)	28,848,000	28,348,000

CONSOLIDATED_STATEMENTS_OF_STO

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $)	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
In Thousands, except Share data
Balance at Dec. 31, 2010	$381,502	$208	$374,981	($8,706)	$15,019
Balance (in shares) at Dec. 31, 2010	'	20,773,000	'	'	'
Net income	14,656	'	'	'	14,656
Foreign currency translation adjustment	25	'	'	25	'
Net change in unrealized gain (loss) on investments	113	'	'	113	'
Exercise of stock options (in shares)	'	198,000	'	'	'
Exercise of stock options	6,214	2	6,212	'	'
Restricted stock grants (in shares)	'	197,000	'	'	'
Restricted stock grants	1	1	0	'	'
Restricted stock grants surrendered (in shares)	'	-63,000	'	'	'
Restricted stock grants surrendered	-2,307	'	-2,307	'	'
Stock compensation expense, net of forfeitures	8,056	'	8,056	'	'
Stock issued for equity offering (in shares)	'	4,313,000	'	'	'
Stock issued for equity offering	247,924	43	247,881	'	'
Employee stock purchase plan (in shares)	'	8,000	'	'	'
Employee stock purchase plan	452	'	452	'	'
Excess tax benefit from stock-based compensation	2,541	'	2,541	'	'
Balance at Dec. 31, 2011	659,177	254	637,816	-8,568	29,675
Balance (in shares) at Dec. 31, 2011	'	25,426,000	'	'	'
Net income	9,915	'	'	'	9,915
Foreign currency translation adjustment	1,277	'	'	1,277	'
Net change in unrealized gain (loss) on investments	773	'	'	773	'
Exercise of stock options (in shares)	'	273,000	'	'	'
Exercise of stock options	9,196	2	9,194	'	'
Restricted stock grants (in shares)	'	855,000	'	'	'
Restricted stock grants	0	8	-8	'	'
Restricted stock grants surrendered (in shares)	'	-96,000	'	'	'
Restricted stock grants surrendered	-4,204	'	-4,204	'	'
Stock compensation expense, net of forfeitures	12,207	'	12,207	'	'
Employee stock purchase plan (in shares)	'	10,000	'	'	'
Employee stock purchase plan	749	'	749	'	'
Consideration for LoopNet, Inc. (in shares)	'	1,880,000	'	'	'
Consideration for LoopNet, Inc.	137,055	19	137,036	'	'
Excess tax benefit from stock-based compensation	198	'	198	'	'
Balance at Dec. 31, 2012	826,343	283	792,988	-6,518	39,590
Balance (in shares) at Dec. 31, 2012	'	28,348,000	'	'	'
Net income	29,734	'	'	'	29,734
Foreign currency translation adjustment	610	'	'	610	'
Net change in unrealized gain (loss) on investments	378	'	'	378	'
Exercise of stock options (in shares)	'	409,000	'	'	'
Exercise of stock options	16,823	3	16,820	'	'
Restricted stock grants (in shares)	'	238,000	'	'	'
Restricted stock grants	0	2	-2	'	'
Restricted stock grants surrendered (in shares)	'	-158,000	'	'	'
Restricted stock grants surrendered	-8,469	'	-8,469	'	'
Stock compensation expense, net of forfeitures	41,403	'	41,403	'	'
Employee stock purchase plan (in shares)	'	11,000	'	'	'
Employee stock purchase plan	1,455	'	1,455	'	'
Excess tax benefit from stock-based compensation	19,585	'	19,585	'	'
Balance at Dec. 31, 2013	$927,862	$288	$863,780	($5,530)	$69,324
Balance (in shares) at Dec. 31, 2013	'	28,848,000	'	'	'

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating activities:	'	'	'
Net income	$29,734	$9,915	$14,656
Adjustments to reconcile net income to net cash provided by operating activities:	'	'	'
Depreciation	12,495	10,053	8,435
Amortization	27,563	22,699	4,417
Amortization of debt issuance costs	3,014	1,989	0
Property and equipment write-off	104	122	628
Excess tax benefit from stock-based compensation	-19,585	-198	-2,541
Stock-based compensation expense	41,549	12,282	8,103
Deferred consideration settlement	0	0	-1,207
Deferred income tax expense (benefit), net	-12,740	13,643	-17,104
Provision for losses on accounts receivable	2,317	1,456	1,525
Changes in operating assets and liabilities, net of acquisitions:	'	'	'
Accounts receivable	-6,607	1,295	-4,573
Income taxes payable	29,295	7,598	7,992
Prepaid expenses and other current assets	2,934	-3,316	1,046
Deposits and other assets	399	1,172	-154
Accounts payable and other liabilities	-3,882	1,629	2,228
Deferred revenue	1,708	5,787	4,334
Net cash provided by operating activities	108,298	86,126	27,785
Investing activities:	'	'	'
Proceeds from sale and settlement of investments	76	15,365	4,911
Proceeds from sale of building, net	0	0	83,553
Purchases of property and equipment and other assets	-19,042	-14,834	-15,013
Acquisitions, net of cash acquired	0	-640,929	-15,085
Net cash provided by (used in) investing activities	-18,966	-640,398	58,366
Financing activities:	'	'	'
Proceeds from long-term debt	0	175,000	0
Payments of long-term debt	-17,500	-4,375	0
Payments of debt issuance costs	0	-11,546	0
Payments of deferred consideration	-1,344	0	-2,100
Excess tax benefit from stock-based compensation	19,585	198	2,541
Repurchase of restricted stock to satisfy tax withholding obligations	-8,469	-4,204	-2,307
Proceeds from equity offering, net of transaction costs	0	0	247,924
Proceeds from exercise of stock options and employee stock purchase plan	18,133	9,868	6,622
Net cash provided by financing activities	10,405	164,941	252,680
Effect of foreign currency exchange rates on cash and cash equivalents	189	78	44
Net increase (decrease) in cash and cash equivalents	99,926	-389,253	338,875
Cash and cash equivalents at beginning of year	156,027	545,280	206,405
Cash and cash equivalents at end of year	$255,953	$156,027	$545,280

ORGANIZATION

ORGANIZATION	12 Months Ended
	Dec. 31, 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	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	'
	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	Basis of Presentation
	The 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
	The preparation of financial statements in conformity with U.S. generally accepted accounting principles (“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 consolidated statements of cash flows have been reclassified to conform to the Company’s current presentation.
	Revenue Recognition
	The Company primarily derives revenues by providing access to its proprietary database of commercial real estate information. The Company generally charges a fixed monthly amount for its subscription-based services. Subscription contract rates are based on the number of sites, number of users, organization size, the client’s business focus, geography and the number of services to which a client subscribes. A majority of the subscription-based license agreements typically have a term of one year and renew automatically.
	Revenue is recognized when (1) there is persuasive evidence of an arrangement, (2) the fee is fixed and determinable, (3) services have been rendered and payment has been contractually earned and (4) collectability is reasonably assured.
	Revenues from subscription-based services are recognized on a straight-line basis over the term of the agreement. Deferred revenue results from advance cash receipts from customers or amounts billed in advance to customers from the sales of subscription licenses and is recognized over the term of the license agreement.
	Cost of Revenues
	Cost of revenues principally consists of salaries and related expenses for the Company’s researchers who collect and analyze the commercial real estate data that is the basis for the Company’s information, analytics and marketing services. Additionally, cost of revenues includes the cost of data from third party data sources, credit card and other transaction fees relating to processing customer transactions, which are expensed as incurred, and the amortization of acquired trade names and database technology.
	2	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED)
	Foreign Currency Translation
	The Company’s functional currency in its foreign locations is the local currency. Assets and liabilities are translated into U.S. dollars 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 consolidated statements of operations. There were no material gains or losses from foreign currency exchange transactions for the years ended December 31, 2011, 2012 and 2013.
	Accumulated Other Comprehensive Loss
	The components of accumulated other comprehensive loss were as follows (in thousands):
		Year Ended December 31,
		2012			2013
	Foreign currency translation adjustment	$	(4,613	)	$	(4,003	)
	Accumulated net unrealized loss on investments, net of tax	(1,905		)	(1,527		)
	Total accumulated other comprehensive loss	$	(6,518	)	$	(5,530	)
	There were no amounts reclassified out of accumulated other comprehensive loss to the consolidated statements of operations for the years ended December 31, 2011, 2012 and 2013, respectively.
	Advertising Costs
	The Company expenses advertising costs as incurred. E-commerce advertising expenses were approximately $2.5 million, $4.4 million and $5.7 million for the years ended December 31, 2011, 2012 and 2013, respectively.
	Income Taxes
	Deferred income taxes result from temporary differences between the tax basis of assets and liabilities and the basis reported in the Company’s consolidated financial statements. Deferred tax liabilities and assets are determined based on the difference between the financial statement and the tax basis of assets and liabilities using enacted rates expected to be in effect during the year in which the differences reverse. Valuation allowances are provided against assets, including net operating losses, if it is anticipated that some or all of an asset may not be realized through future taxable earnings or implementation of tax planning strategies. Interest and penalties related to income tax matters are recognized in income tax expense.
	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
	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 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, subject to certain approvals under the CoStar Group, Inc. 2007 Stock Incentive Plan. As of March 31, 2013, the Company initially determined that it was probable that the performance condition for these performance-based restricted common stock awards would be met by the March 31, 2017 forfeiture date. As of December 31, 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 $21.8 million of stock-based compensation expense related to performance-based restricted common stock for the year ended December 31, 2013. There was no stock-based compensation expense related to performance-based restricted common stock recorded for the years ended December 31, 2011 and December 31, 2012. The Company expects to record additional estimated unrecognized stock-based compensation expense related to performance-based restricted common stock of approximately $2.1 million 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 $6.6 million, $9.9 million and $18.1 million for the years ended December 31, 2011, 2012 and 2013, respectively. There were approximately $2.5 million, $198,000 and $19.6 million of excess tax benefits realized from stock options exercised and restricted stock awards vested for the years ended December 31, 2011, 2012 and 2013, respectively.
	Stock-based compensation expense for stock options and restricted stock issued under equity incentive plans and stock purchases under the ESPP included in the Company's results of operations were as follows (in thousands):
		Year Ended December 31,
		2011			2012			2013
	Cost of revenues	$	1,635		$	2,556		$	4,553
	Selling and marketing	1,339			1,966			4,954
	Software development	1,130			2,241			7,244
	General and administrative	3,999			5,519			24,798
	Total stock-based compensation	$	8,103		$	12,282		$	41,549
	Cash and Cash Equivalents
	The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. Cash equivalents consist of money market fund investments and commercial paper. As of December 31, 2012 and 2013, cash of approximately $0 and $105,000, respectively, was held to support letters of credit for security deposits.
	2	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED)
	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 consisted 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 were classified as current in the Company’s consolidated balance sheets because they represented 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 value.
	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. No single customer accounted for more than 5% of the Company’s revenues for each of the years ended December 31, 2011, 2012 and 2013. The carrying amount of the accounts receivable approximates the net realizable value. The carrying value of the accounts receivable, accounts payable, accrued expenses and long-term debt approximates fair value.
	Accounts Receivable, Net of Allowance for Doubtful Accounts
	Accounts receivable are recorded at the invoiced amount. Accounts receivable payment terms vary and amounts due from customers are stated in the financial statements net of an allowance for doubtful accounts. The allowance for doubtful accounts is based on the Company’s assessment of the collectability of customer accounts. The Company regularly reviews the allowance by considering factors such as historical experience, the aging of the balances, and current economic conditions that may affect a customer’s ability to pay.
	Property and Equipment
	Property and equipment are stated at cost. All repairs and maintenance costs are expensed as incurred. Depreciation and amortization are calculated on a straight-line basis over the following estimated useful lives of the assets:
	Leasehold improvements		Shorter of lease term or useful life
	Furniture and office equipment		Five to ten years
	Research vehicles		Five years
	Computer hardware and software		Two to five years
	Qualifying internal-use software costs incurred during the application development stage, which consists primarily of outside services, purchased software license costs and internal product development costs are capitalized and amortized over the estimated useful life of the asset. All other costs are expensed as incurred.
	2	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED)
	Goodwill, Intangibles and Other Assets
Goodwill represents the excess of costs over the fair value of assets of acquired businesses. Goodwill and intangible assets acquired in a business combination and determined to have an indefinite useful life are not amortized, but instead tested for impairment at least annually by reporting unit. The Company’s operating segments, U.S. and International, are the reporting units tested for potential impairment. To determine whether it is necessary to perform the two-step goodwill impairment test, the Company may first assess qualitative factors to evaluate whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If the Company concludes that it is more likely than not that the fair value of a reporting unit is less than its carrying amount or if the Company elects not to assess qualitative factors, then the Company performs the two-step process. The first step is to determine the fair value of each reporting unit. The estimate of the fair value of each reporting unit is based on a projected discounted cash flow model that includes significant assumptions and estimates including the Company's discount rate, growth rate and future financial performance. Assumptions about the discount rate are based on a weighted average cost of capital for comparable companies. Assumptions about the growth rate and future financial performance of a reporting unit are based on the Company's forecasts, business plans, economic projections and anticipated future cash flows. The fair value of each reporting unit is compared to the carrying amount of the reporting unit. If the carrying value of the reporting unit exceeds the fair value, then the second step of the process is performed to measure the impairment loss. The impairment loss is measured based on a projected discounted cash flow method using a discount rate determined by the Company’s management to be commensurate with the risk in its current business model.
To determine whether it is necessary to perform the quantitative impairment test for indefinite-lived intangible assets, the Company may first assess qualitative factors to evaluate whether it is more likely than not that the fair value of the indefinite-lived intangible assets is less than the carrying amount. If the Company concludes that it is more likely than not that the fair value of the indefinite-lived intangible assets is less than the carrying amount or if the Company elects not to assess qualitative factors, then the Company performs the quantitative impairment test similar to the test performed on goodwill discussed above.
Intangible assets with estimable useful lives that arose from acquisitions on or after July 1, 2001 are amortized over their respective estimated useful lives using a method of amortization that reflects the pattern in which the economic benefits of the intangible assets are consumed or otherwise used up, and are reviewed at least annually for impairment.
Acquired database technology, customer base and trade names and other are related to the Company’s acquisitions (see Notes 3, 7 and 8). With the exception of the acquired trade name recorded in connection with the acquisition of LoopNet, acquired database technology and trade names and other are amortized on a straight-line basis over periods ranging from two to ten years. The acquired trade name recorded in connection with the LoopNet acquisition has an indefinite estimated useful life and is not amortized, but is subject to annual impairment tests. The acquired intangible asset characterized as customer base consists of one distinct intangible asset composed of acquired customer contracts and the related customer relationships. Acquired customer bases are typically amortized on an accelerated basis related to the expected economic benefit of the intangible asset. The cost of capitalized building photography is amortized on a straight-line basis over five years.
Long-Lived Assets
Long-lived assets, such as property, plant, and equipment, and purchased intangibles subject to amortization, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to estimated undiscounted future cash flows expected to be generated by the asset or asset group. If the carrying amount of an asset exceeds its estimated future cash flows, an impairment charge is recognized in the amount by which the carrying amount of the asset exceeds the fair value of the asset.
Assets to be disposed of would be separately presented in the balance sheet and reported at the lower of the carrying amount or fair value less costs to sell, and would no longer be depreciated. The assets and liabilities of a disposal group classified as held for sale would be presented separately in the appropriate asset and liability sections of the balance sheet.
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 $302,000 and $111,000 as of December 31, 2012 and 2013, respectively. These capitalized product development costs are included in intangible and other assets in the Company’s 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 $80,000, $191,000 and $191,000 for the years ended December 31, 2011, 2012 and 2013, respectively.
Debt Issuance Costs
Costs incurred in connection with the issuance of long-term debt are capitalized and amortized as interest expense over the term of the related debt using the effective interest method. The Company had capitalized debt issuance costs of approximately $9.6 million and $6.5 million as of December 31, 2012 and 2013, 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 9 for additional information regarding the financing commitment with J.P. Morgan Bank and the Credit Agreement. No amortization expense for debt issuance costs was recognized by the Company for the year ended December 31, 2011. The Company amortized debt issuance costs of approximately $2.0 million and $3.0 million for the years ended December 31, 2012 and 2013, respectively.
Recent Accounting Pronouncements
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, but the Company provided additional disclosures in its financial statements.
There are no accounting pronouncements that have been recently issued but not yet adopted by the Company that would have a material impact on the Company’s results of operations or financial position.

ACQUISITION

ACQUISITION	12 Months Ended
	Dec. 31, 2013
Business Combinations [Abstract]	'
ACQUISITIONS	'
	ACQUISITION
	On April 30, 2012, the Company acquired 100% of the outstanding stock of 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 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.
	3	ACQUISITION — (CONTINUED)
	As a result of the LoopNet acquisition, the Company recorded approximately $14.2 million and $5.2 million in acquisition-related costs for the years ended December 31, 2011 and 2012, respectively. These costs were directly related to acquiring LoopNet and were expensed as incurred and recorded in general and administrative expense. There were no acquisition-related costs recorded for the year ended December 31, 2013 related to the LoopNet acquisition.
	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. On March 28, 2012, the Company and LoopNet entered into an agreement to sell LoopNet's interest in Xceligent to DMG Information (“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	12 Months Ended
	Dec. 31, 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 consisted 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 were classified as current in the Company’s consolidated balance sheets because they represented the investment of cash that was available for current operations. Long-term investments consist of variable rate debt instruments with an auction reset feature, referred to as ARS. Investments are carried at fair market value.
	Scheduled maturities of investments classified as available-for-sale as of December 31, 2013 are as follows (in thousands):
	Maturity		Fair Value
	Due in:
	2014		$	—
	2015 — 2018		853
	2019 — 2023		—
	2024 and thereafter		21,137
	Available-for-sale investments		$	21,990
	The Company had no realized gains on its investments for the years ended December 31, 2011, 2012 and 2013, respectively. The Company had no realized losses on its investments for the years ended December 31, 2011, 2012 and 2013, respectively. Realized gains and losses from the sale of available-for-sale securities are determined on a specific-identification basis.
	Changes in unrealized holding gains and losses, net of the related tax effect, on available-for-sale securities are excluded from earnings and are reported as a separate component of accumulated other comprehensive income (loss) in stockholders’ equity until realized. A decline in market value of any available-for-sale security below cost that is deemed to be other-than-temporary results in a reduction in carrying amount to fair value. The impairment is charged to earnings and a new cost basis for the security is established. Dividend and interest income are recognized when earned.
	As of December 31, 2013, the amortized cost basis and fair value of investments classified as available-for-sale were as follows (in thousands):
		Amortized			Gross			Gross			Fair Value
		Cost			Unrealized			Unrealized
					Gains			Losses
	Auction rate securities	$	23,517		$	411		$	(1,938	)	$	21,990
	Available-for-sale investments	$	23,517		$	411		$	(1,938	)	$	21,990
	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 Value
		Cost			Unrealized			Unrealized
					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 December 31, 2012 and 2013 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 December 31, 2012 and 2013. 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 more than twelve months were as follows (in thousands):
		December 31,
		2012						2013
		Aggregate			Gross			Aggregate			Gross
		Fair			Unrealized			Fair			Unrealized
		Value			Losses			Value			Losses
	Government-sponsored enterprise obligations	$	37		$	—		$	—		$	—
	Auction rate securities	21,119			(2,006		)	21,137			(1,938		)
	Investments in an unrealized loss position	$	21,156		$	(2,006	)	$	21,137		$	(1,938	)
	The Company did not have any investments in an unrealized loss position for less than twelve months as of December 31, 2012 and 2013, respectively.

FAIR_VALUE

FAIR VALUE	12 Months Ended
	Dec. 31, 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 December 31, 2013 (in thousands):
		Level 1			Level 2		Level 3		Total
	Assets:
	Cash	$	134,989		$	—	$	—	$	134,989
	Money market funds	50,593			—		—		50,593
	Commercial paper	70,371			—		—		70,371
	Auction rate securities	—			—		21,990		21,990
	Total assets measured at fair value	$	255,953		$	—	$	21,990	$	277,943
	Liabilities:
	Deferred consideration	$	—		$	—	$	1,344	$	1,344
	Total liabilities measured at fair value	$	—		$	—	$	1,344	$	1,344
	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.
	5	FAIR VALUE — (CONTINUED)
	The following table summarizes changes in fair value of the Company’s Level 3 assets from December 31, 2007 to December 31, 2013 (in thousands):
		Auction
		Rate
		Securities
	Balance at December 31, 2007	$	53,975
	Increase in unrealized loss included in accumulated other comprehensive loss	(3,710		)
	Settlements	(20,925		)
	Balance at December 31, 2008	29,340
	Decrease in unrealized loss included in accumulated other comprehensive loss	684
	Settlements	(300		)
	Balance at December 31, 2009	29,724
	Decrease in unrealized loss included in accumulated other comprehensive loss	40
	Settlements	(575		)
	Balance at December 31, 2010	29,189
	Decrease in unrealized loss included in accumulated other comprehensive loss	245
	Settlements	(4,850		)
	Balance at December 31, 2011	24,584
	Auction rate securities upon acquisition	442
	Decrease in unrealized loss included in accumulated other comprehensive loss	836
	Settlements	(4,200		)
	Balance at December 31, 2012	21,662
	Decrease in unrealized loss included in accumulated other comprehensive loss	378
	Settlements	(50		)
	Balance at December 31, 2013	$	21,990
	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 December 31, 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 consolidated balance sheet as of December 31, 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 December 31, 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 December 31, 2012 and 2013 was approximately 5.1% and 4.9%, 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 December 31, 2013, the Company determined there was a decline in the fair value of its ARS investments of approximately $1.5 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 December 31, 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 $1.3 million as of December 31, 2013 and included deferred cash payments in connection with acquisitions LoopNet completed in 2010 including: (i) 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 December 31, 2013 of approximately $1.0 million; and (ii) 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 December 31, 2013 of approximately $344,000. On March 28, 2013, the Company made a payment of $1.0 million to the sellers of LandsofAmerica based on the achievement of financial and operational milestones in 2012 and a payment of approximately $344,000 to the sellers of Reaction Web based on the achievement of revenue milestones in 2012.
	The following table summarizes changes in fair value of the Company’s Level 3 liabilities from December 31, 2011 to December 31, 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 for 2013	384
Payments made in 2013	(1,344		)
Balance at December 31, 2013	$	1,344
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.
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 December 31, 2012 was approximately 23.5%. As of December 31, 2013, the Company recorded a liability for the entire amount of undiscounted deferred consideration to be paid on March 31, 2014. Selecting another discount rate within the range used in the discounted cash flow model in 2012 would not result in a significant change to the fair value of the deferred consideration.

PROPERTY_AND_EQUIPMENT

PROPERTY AND EQUIPMENT	12 Months Ended
	Dec. 31, 2013
Property, Plant and Equipment [Abstract]	'
PROPERTY AND EQUIPMENT	'
	PROPERTY AND EQUIPMENT
	Property and equipment consists of the following (in thousands):
		December 31,
		2012			2013
	Leasehold improvements	$	28,527		$	36,933
	Furniture, office equipment and research vehicles	25,837			27,395
	Computer hardware and software	36,688			36,391
		91,052			100,719
	Accumulated depreciation and amortization	(44,744		)	(43,000		)
	Property and equipment, net	$	46,308		$	57,719
	Depreciation expense for property and equipment was approximately $8.4 million, $10.1 million and $12.5 million for the years ended December 31, 2011, 2012 and 2013, respectively.

GOODWILL

GOODWILL	12 Months Ended
	Dec. 31, 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	—		509		509
	Goodwill, December 31, 2013	$	692,639	$	25,948	$	718,587
	The Company recorded goodwill of approximately $625.2 million in connection with the April 30, 2012 acquisition of LoopNet.
	During the fourth quarters of 2011, 2012 and 2013, the Company completed the annual impairment test of goodwill and concluded that goodwill was not impaired.

INTANGIBLES_AND_OTHER_ASSETS

INTANGIBLES AND OTHER ASSETS	12 Months Ended
	Dec. 31, 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):
		December 31,						Weighted- Average
								Amortization Period
		2012			2013			(in years)
	Capitalized product development cost	$	2,140		$	2,140		4
	Accumulated amortization	(1,838		)	(2,029		)
	Capitalized product development cost, net	302			111
	Building photography	12,474			13,743			5
	Accumulated amortization	(11,639		)	(12,005		)
	Building photography, net	835			1,738
	Acquired database technology	77,328			77,368			5
	Accumulated amortization	(29,673		)	(41,073		)
	Acquired database technology, net	47,655			36,295
	Acquired customer base	130,683			130,960			10
	Accumulated amortization	(59,218		)	(74,734		)
	Acquired customer base, net	71,465			56,226
	Acquired trade names and other (1)	59,255			59,336			7
	Accumulated amortization	(8,880		)	(9,234		)
	Acquired trade names and other, net	50,375			50,102
	Intangibles and other assets, net	$	170,632		$	144,472
	(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.
	Amortization expense for intangibles and other assets was approximately $4.4 million, $22.7 million and $27.6 million for the years ended December 31, 2011, 2012 and 2013, respectively.
	In the aggregate, amortization for intangibles and other assets existing as of December 31, 2013 for future periods is expected to be approximately $23.5 million, $20.8 million, $18.9 million, $10.0 million and $5.1 million for the years ending December 31, 2014, 2015, 2016, 2017 and 2018, respectively.
	During the fourth quarter of 2013, the Company completed the annual impairment test of the acquired trade name recorded in connection with the LoopNet acquisition and concluded that this indefinite-lived intangible asset was not impaired.

LONGTERM_DEBT

LONG-TERM DEBT	12 Months Ended
	Dec. 31, 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 Level 3 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.
	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 1.00% 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 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 December 31, 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, 2013, the Company was not required to make an Excess Cash Flow payment.
	In connection with obtaining the term loan facility and revolving credit 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 December 31, 2012 and 2013, no amounts were outstanding under the revolving credit facility. Total interest expense for the term loan facility was approximately $0, $4.8 million and $6.9 million for the years ended December 31, 2011, 2012 and 2013, respectively. Interest expense included amortized debt issuance costs of approximately $0, $2.0 million and $3.0 million for the years ended December 31, 2011, 2012 and 2013, respectively. Total interest paid for the term loan facility was approximately $0, $2.5 million and $4.3 million for the years ended December 31, 2011, 2012 and 2013, respectively.
	9	LONG-TERM DEBT — (CONTINUED)
	Maturities of the Company's borrowings under the Credit Agreement for each of the next four years as of December 31, 2013 are as follows (in thousands):
	Year ending December 31,	Maturities
	Due in:
	2014	$	24,063
	2015	32,812
	2016	61,250
	2017	35,000
	Long-term debt, including current maturities	$	153,125

INCOME_TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
INCOME TAXES	'
	INCOME TAXES
	The components of the provision (benefit) for income taxes attributable to operations consist of the following (in thousands):
		Year Ended December 31,
		2011			2012			2013
	Current:
	Federal	$	22,779		$	(2,260	)	$	26,516
	State	2,226			1,974			3,996
	Foreign	12			55			31
	Total current	25,017			(231		)	30,543
	Deferred:
	Federal	(14,661		)	15,512			(10,919		)
	State	(2,425		)	(2,067		)	(1,849		)
	Foreign	(18		)	5			28
	Total deferred	(17,104		)	13,450			(12,740		)
	Total provision for income taxes	$	7,913		$	13,219		$	17,803
	10	INCOME TAXES — (CONTINUED)
	The components of deferred tax assets and liabilities consists of the following (in thousands):
		December 31,
		2012			2013
	Deferred tax assets:
	Reserve for bad debts	$	1,106		$	1,274
	Accrued compensation	4,830			6,725
	Stock compensation	4,946			13,381
	Net operating losses	20,431			17,457
	Accrued reserve and other	6,007			4,284
	Unrealized loss on securities	928			786
	Deferred rent	1,845			4,329
	Deferred revenue	1,220			1,538
	Deferred gain from sale of building	12,386			11,499
	Total deferred tax assets	53,699			61,273
	Deferred tax liabilities:
	Prepaids	(1,433		)	(1,096		)
	Depreciation	(3,676		)	(6,033		)
	Intangibles	(62,915		)	(55,284		)
	Total deferred tax liabilities	(68,024		)	(62,413		)
	Net deferred tax liabilities, prior to valuation allowance	(14,325		)	(1,140		)
	Valuation allowance	(10,490		)	(10,936		)
	Net deferred tax liabilities	$	(24,815	)	$	(12,076	)
	As of December 31, 2012 and 2013, a valuation allowance has been established for certain deferred tax assets due to the uncertainty of realization. The valuation allowance as of December 31, 2012 and 2013 includes an allowance for unrealized losses on ARS investments, foreign deferred tax assets and certain state net operating loss carryforwards. The valuation allowance for the deferred tax asset for unrealized losses on ARS has been recorded as an adjustment to accumulated other comprehensive loss.
	The Company established the valuation allowance because it is more likely than not that a portion of the deferred tax asset for certain items will not be realized based on the weight of available evidence. A valuation allowance was established for the unrealized losses on securities as the Company has not historically generated capital gains, and it is uncertain whether the Company will generate sufficient capital gains in the future to absorb the capital losses. In 2011, the Company sold the office building located at 1331 L Street, NW, in downtown Washington, DC (the “DC Office Building") and the sale generated capital gains, but the Company does not expect to engage in similar transactions on a regular basis. The Company continues to maintain a valuation allowance as of December 31, 2013, for the unrealized losses on securities because it is uncertain as to whether the losses will be realized in a year such that the losses could be carried back to offset the gain from the Company’s sale of the DC Office Building. A valuation allowance was established for the foreign deferred tax assets due to the cumulative loss in recent years in those jurisdictions. The Company has not had sufficient taxable income historically to utilize the foreign deferred tax assets, and it is uncertain whether the Company will generate sufficient taxable income in the future to utilize the deferred tax assets. Similarly, the Company has established a valuation allowance for net operating losses in certain states where it is uncertain whether the Company will generate sufficient taxable income to utilize the net operating losses before they expire.
	The Company’s change in valuation allowance was an increase of approximately $5.2 million for the year ended December 31, 2012 and an increase of approximately $446,000 for the year ended December 31, 2013. The increase for the year ended December 31, 2013 is primarily due to the increase in the valuation allowance for foreign deferred tax assets of approximately $765,000 partially offset by a decrease in the valuation allowance for deferred tax assets of approximately $319,000 primarily related to state net operating loss carryforwards.
	10	INCOME TAXES — (CONTINUED)
	The Company had U.S. income before income taxes of approximately $29.1 million, $36.1 million and $53.2 million for the years ended December 31, 2011, 2012 and 2013, respectively. The Company had foreign losses of approximately $6.6 million, $13.0 million and $5.6 million for the years ended December 31, 2011, 2012 and 2013, respectively.
	The Company’s provision for income taxes resulted in effective tax rates that varied from the statutory federal income tax rate as follows (in thousands):
		Year Ended December 31,
		2011			2012			2013
	Expected federal income tax provision at statutory rate	$	7,899		$	8,097		$	16,638
	State income taxes, net of federal benefit	(123		)	(1,360		)	885
	Foreign income taxes, net effect	(961		)	(2,971		)	(724		)
	Stock compensation	(143		)	(313		)	(116		)
	Increase in valuation allowance	643			2,978			588
	Nondeductible compensation	448			656			431
	Nondeductible transaction costs	—			5,829			—
	Other adjustments	150			303			101
	Income tax expense, net	$	7,913		$	13,219		$	17,803
	The Company’s U.K. subsidiaries with foreign losses are disregarded entities for U.S. income tax purposes. Accordingly, the losses from these disregarded entities are included in the Company’s consolidated federal income tax provision at the statutory rate. Federal income taxes attributable to income from these disregarded entities are reduced by foreign taxes paid by those disregarded entities.
	The Company paid approximately $19.5 million, $2.6 million, and $6.5 million in income taxes for the years ended December 31, 2011, 2012 and 2013, respectively.
	The Company has net operating loss carryforwards for international income tax purposes of approximately $31.2 million, which do not expire. The Company has federal net operating loss carryforwards of approximately $13.5 million that begin to expire in 2020, state net operating loss carryforwards with a tax value of approximately $4.9 million that begin to expire in 2020 and state income tax credit carryforwards with a tax value of approximately $1.8 million that begin to expire in 2020. The Company realized a cash benefit relating to the use of its tax loss carryforwards of approximately $12.2 million and $4.2 million in 2012 and 2013, respectively.
	The following tables summarize the activity related to the Company’s unrecognized tax benefits (in thousands):
	Unrecognized tax benefit as of December 31, 2010	$	1,766
	Increase for current year tax positions	1,243
	Increase for prior year tax positions	445
	Expiration of the statute of limitation for assessment of taxes	(107		)
Unrecognized tax benefit as of December 31, 2011	3,347
Increase for current year tax positions	792
Decrease for prior year tax positions	(161		)
Expiration of the statute of limitation for assessment of taxes	(69		)
Unrecognized tax benefit as of December 31, 2012	3,909
Increase for current year tax positions	66
Increase for prior year tax positions	2,037
Expiration of the statute of limitation for assessment of taxes	(55		)
Unrecognized tax benefit as of December 31, 2013	$	5,957
10	INCOME TAXES — (CONTINUED)
Approximately $1.6 million of the unrecognized tax benefit as of each of December 31, 2012 and 2013, would favorably affect the annual effective tax rate, if recognized in future periods. The Company recognized $39,000, $58,000 and $62,000 for interest and penalties in its consolidated statements of operations for the years ended December 31, 2011, 2012 and 2013, respectively. The Company had liabilities of $284,000, $342,000 and $404,000 for interest and penalties in its consolidated balance sheets as of December 31, 2011, 2012 and 2013, respectively. The Company does not anticipate the amount of the unrecognized tax benefits to change significantly over the next twelve months.
The Company’s federal and state income tax returns for tax years 2010 through 2012 remain open to examination. The Company’s U.K. income tax returns for tax years 2007 through 2012 remain open to examination.
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	12 Months Ended
	Dec. 31, 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. Rent expense for the years ended December 31, 2011, 2012 and 2013 was approximately $13.3 million, $16.7 million and $18.3 million, respectively.
	Future minimum lease payments as of December 31, 2013 are as follows (in thousands):
	2014	$	17,004
	2015	15,128
	2016	14,104
	2017	14,317
	2018	13,916
	2019 and thereafter	69,475
	Total future minimum lease payments	$	143,944
	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 9 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 did not maximize value to LoopNet stockholders, (iii) LoopNet and the Company made incomplete or materially misleading disclosures about the 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 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 rescheduled the show cause hearing for February 11, 2014, and then rescheduled it again for May 13, 2014.
	11	COMMITMENTS AND CONTINGENCIES — (CONTINUED)
	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 against Civix for breach of contract, alleging Civix viloated 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 against Civix for breach of contract, alleging Civix violated 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. On November 25, 2013, Civix submitted its expert’s report of damages, which estimated the payment it deemed appropriate in the event that the Company is found liable of infringement. The Company believes that Civix’s calculation of damages is based on improper assumptions and miscalculations, and is otherwise unsupported. The Company submitted its own expert’s report of damages, which concluded that the appropriate payment to be made in the event that the Company is found liable of infringement is significantly less than Civix’s estimate of appropriate damages. Moreover, the Company’s expert's report of damages concluded that while Civix’s calculation of damages was fundamentally flawed and should not be used to determine damages, simply applying certain necessary adjustments to Civix's calculation as outlined in the Company’s report resulted in a significant reduction in Civix’s calculation of damages to approximately $3.7 million. On November 5, 2013 the Company offered to settle all outstanding litigation with Civix for $600,000. At this time the Company cannot predict the outcome of its litigation with Civix, but the Company intends to vigorously defend itself against Civix’s claims.  While the Company believes it has meritorious defenses against Civix’s claims, the Company estimates that, based on the Company’s adjusted calculation of Civix’s alleged damages, the matter could result in a loss of up to $3.1 million in excess of the amount accrued.
	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 consolidated financial statements for unfavorable results, if any, other than described above. Legal defense costs are expensed as incurred.

SEGMENT_REPORTING

SEGMENT REPORTING	12 Months Ended
	Dec. 31, 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 SuiteTM and FOCUSTM 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 and no longer offered FOCUS to new clients beginning in 2013. 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.
	Summarized information by operating segment was as follows (in thousands):
		Year Ended December 31,
		2011			2012			2013
	Revenues
	United States	$	233,381		$	330,805		$	420,817
	International
	External customers	18,357			19,131			20,126
	Intersegment revenue	1,140			1,514			339
	Total international revenue	19,497			20,645			20,465
	Intersegment eliminations	(1,140		)	(1,514		)	(339		)
	Total revenues	$	251,738		$	349,936		$	440,943
	EBITDA
	United States	$	38,099		$	70,199		$	97,348
	International	(3,476		)	(10,007		)	(3,136		)
	Total EBITDA	$	34,623		$	60,192		$	94,212
	Reconciliation of EBITDA to net income
	EBITDA	$	34,623		$	60,192		$	94,212
	Purchase amortization in cost of revenues	(1,353		)	(8,634		)	(11,883		)
	Purchase amortization in operating expenses	(2,237		)	(13,607		)	(15,183		)
	Depreciation and other amortization	(9,262		)	(10,511		)	(12,992		)
	Interest income	798			526			326
	Interest expense	—			(4,832		)	(6,943		)
	Income tax expense, net	(7,913		)	(13,219		)	(17,803		)
	Net income	$	14,656		$	9,915		$	29,734
	Intersegment revenue is attributable to services performed for the Company’s wholly owned subsidiary, Property and Portfolio Research (“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.
	12	SEGMENT REPORTING — (CONTINUED)
	There were no costs allocated to U.S. EBITDA for the years ended December 31, 2011 and 2012. U.S. EBITDA includes an allocation of approximately $800,000 for the year ended December 31, 2013. 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 $800,000, $5.3 million and $400,000 for the years ended December 31, 2011, 2012 and 2013, respectively. This allocation represents costs incurred for U.S. employees involved in management and expansion activities of the Company’s International operating segment.
	Summarized information by operating segment consists of the following (in thousands):
		December 31,
		2012			2013
	Property and equipment, net
	United States	$	42,480		$	53,733
	International	3,828			3,986
	Total property and equipment, net	$	46,308		$	57,719
	Goodwill
	United States	$	692,639		$	692,639
	International	25,439			25,948
	Total goodwill	$	718,078		$	718,587
	Assets
	United States	$	1,215,949		$	1,311,292
	International	40,933			43,464
	Total operating segment assets	$	1,256,882		$	1,354,756
	Reconciliation of operating segment assets to total assets
	Total operating segment assets	$	1,256,882		$	1,354,756
	Investment in subsidiaries	(18,344		)	(18,344		)
	Intersegment receivables	(73,399		)	(79,430		)
	Total assets	$	1,165,139		$	1,256,982
	Liabilities
	United States	$	335,855		$	324,626
	International	70,108			79,266
	Total operating segment liabilities	$	405,963		$	403,892
	Reconciliation of operating segment liabilities to total liabilities
	Total operating segment liabilities	$	405,963		$	403,892
	Intersegment payables	(67,167		)	(74,772		)
	Total liabilities	$	338,796		$	329,120

STOCKHOLDERS_EQUITY

STOCKHOLDERS' EQUITY	12 Months Ended
	Dec. 31, 2013
Stockholders' Equity Note [Abstract]	'
STOCKHOLDERS' EQUITY	'
	STOCKHOLDERS’ EQUITY
	Preferred Stock
	The Company has 2,000,000 shares of preferred stock, $0.01 par value, authorized for issuance as of December 31, 2013. The Board of Directors may issue the preferred stock from time to time as shares of one or more classes or series.
	Common Stock
	The Company has 60,000,000 shares of common stock, $0.01 par value, authorized for issuance. On June 5, 2012, the Company amended and restated its Restated Certificate of Incorporation to increase the authorized shares of common stock by 30,000,000 shares to 60,000,000 shares. Dividends may be declared and paid on the common stock, subject in all cases to the rights and preferences of the holders of preferred stock and authorization by the Board of Directors. In the event of liquidation or winding up of the Company and after the payment of all preferential amounts required to be paid to the holders of any series of preferred stock, any remaining funds shall be distributed among the holders of the issued and outstanding common stock.

NET_INCOME_PER_SHARE

NET INCOME PER SHARE	12 Months Ended
	Dec. 31, 2013
Earnings Per Share [Abstract]	'
NET INCOME PER SHARE	'
	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):
		Year Ended December 31,
		2011		2012		2013
	Numerator:
	Net income	$	14,656	$	9,915	$	29,734
	Denominator:
	Denominator for basic net income per share — weighted-average outstanding shares	23,131		26,533		27,670
	Effect of dilutive securities:
	Stock options and restricted stock	396		416		542
	Denominator for diluted net income per share — weighted-average outstanding shares	23,527		26,949		28,212
	Net income per share — basic	$	0.63	$	0.37	$	1.07
	Net income per share — diluted	$	0.62	$	0.37	$	1.05
	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. Stock options to purchase approximately 2,300 shares that were outstanding as of December 31, 2011 were not included in the computation of diluted net income per share because the exercise price of the stock options was greater than the average share price of the common shares during the period. No stock options to purchase shares were excluded from the calculation of diluted net income per share for the years ended December 31, 2012 and 2013. Additionally, shares of restricted common stock that vest based on Company performance conditions that have not been achieved as of the end of the period are not included in the computation of basic or diluted earnings per share.

EMPLOYEE_BENEFIT_PLANS

EMPLOYEE BENEFIT PLANS	12 Months Ended
	Dec. 31, 2013
Compensation Related Costs [Abstract]	'
EMPLOYEE BENEFIT PLANS	'
	EMPLOYEE BENEFIT PLANS
	Stock Incentive Plans
	In June 1998, the Company’s Board of Directors adopted the 1998 Stock Incentive Plan (as amended, the “1998 Plan”) prior to consummation of the Company’s initial public offering. In April 2007, the Company’s Board of Directors adopted the CoStar Group, Inc. 2007 Stock Incentive Plan (as amended, the “2007 Plan”), subject to stockholder approval, which was obtained on June 7, 2007. All shares of common stock that were authorized for issuance under the 1998 Plan that, as of June 7, 2007, remained available for issuance under the 1998 Plan (excluding shares subject to outstanding awards) were rolled into the 2007 Plan and, as of that date, no shares of common stock were available for new awards under the 1998 Plan. The 1998 Plan continues to govern unexercised and unexpired awards issued under the 1998 Plan prior to June 7, 2007. The 1998 Plan provided for the grant of stock and stock options to officers, directors and employees of the Company and its subsidiaries. Stock options granted under the 1998 Plan could be incentive or non-qualified, and the exercise price for an incentive stock option may not be less than the fair market value of the Company’s common stock on the date of grant. The vesting period of the options and restricted stock grants under the 1998 Plan was determined by the Board of Directors or a committee thereof and was generally three to four years. Upon the occurrence of a Change of Control, as defined in the 1998 Plan, all outstanding unexercisable options and restricted stock grants under the 1998 Plan immediately become exercisable.
	The 2007 Plan provides for the grant of stock options, restricted stock, restricted stock units, and stock appreciation rights to officers, employees, directors and consultants of the Company and its subsidiaries. Stock options granted under the 2007 Plan may be non-qualified or may qualify as incentive stock options. Except in limited circumstances related to a merger or other acquisition, the exercise price for an option may not be less than the fair market value of the Company’s common stock on the date of grant. The vesting period for each grant of options, restricted stock, restricted stock units and stock appreciation rights under the 2007 Plan is determined by the Board of Directors or a committee thereof and is generally three to four years, subject to minimum vesting periods for restricted stock and restricted stock units of at least one year. In some cases, vesting of awards under the 2007 Plan may be based on performance conditions. The Company has issued and/or reserved the following shares of common stock for issuance under the 2007 Plan (including an increase of 1,300,000 shares of common stock pursuant to an amendment to the 2007 Plan approved by the Company’s stockholders on June 2, 2010 and an increase of 900,000 shares of common stock pursuant to an amendment to the 2007 Plan approved by the Company’s stockholders on June 5, 2012): (a) 3,200,000 shares of common stock, plus (b) 121,875 shares of common stock that were authorized for issuance under the 1998 Plan that, as of June 7, 2007, remained available for issuance under the 1998 Plan (not including any Shares that were subject as of such date to outstanding awards under the 1998 Plan), and (c) any shares of common stock subject to outstanding awards under the 1998 Plan as of June 7, 2007, that on or after such date cease for any reason to be subject to such awards (other than by reason of exercise or settlement of the awards to the extent they are exercised for or settled in vested and nonforfeitable shares). Unless terminated sooner, the 2007 Plan will terminate in April 2017, but will continue to govern unexercised and unexpired awards issued under the 2007 Plan prior to that date. Approximately 1.4 million and 1.2 million shares were available for future grant under the 2007 Plan as of December 31, 2012 and 2013, respectively.
	In February 2012, the Compensation Committee (the “Committee”) of the Board of Directors of the Company approved grants of restricted common stock to the executive officers that vest based on the achievement of Company performance conditions. These awards support the Committee’s goals of aligning executive incentives with long-term stockholder value and ensuring that executive officers have a continuing stake in the long-term success of the Company. In May and December of 2012, the Company granted additional shares of restricted common stock that vest based on the achievement of the Company's performance conditions to other employees. These shares of performance-based restricted common stock vest upon the Company’s achievement of $90.0 million of cumulative EBITDA over a period of four consecutive calendar quarters, and are subject to forfeiture in the event the foregoing performance condition is not met by March 31, 2017. The Company granted a total of 399,413 shares of performance-based restricted common stock during the year ended December 31, 2012. There were no shares of performance-based restricted common stock granted by the Company during the year ended December 31, 2013. All of the awards were made under the 2007 Plan and pursuant to the Company’s standard form of restricted stock grant agreement. The number of shares granted was based on the fair market value of the Company’s common stock on the grant date. As of March 31, 2013, the Company initially determined that it was probable that the performance condition for these performance-based restricted common stock awards would be met by the March 31, 2017 forfeiture date. As of December 31, 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, subject to certain approvals under the 2007 Plan. As a result, the Company recorded a total of approximately $21.8 million of stock-based compensation expense related to performance-based restricted common stock for the year ended December 31, 2013. There was no stock-based compensation expense related to performance-based restricted common stock recorded for the years ended December 31, 2011 and 2012.
	15	EMPLOYEE BENEFIT PLANS — (CONTINUED)
	Stock Incentive Plans — (Continued)
	Option activity was as follows:
		Number of		Range of		Weighted-			Weighted-		Aggregate
		Shares		Exercise Price		Average			Average		Intrinsic
						Exercise			Remaining		Value
						Price			Contract		(in thousands)
									Life (in years)
	Outstanding at December 31, 2010	945,696		$17.34 - $55.07		$	36.1
	Granted	111,470		$57.16 - $60.23		$	57.28
	Exercised	(198,132	)	$17.97 - $54.51		$	31.37
	Canceled or expired	(11,932	)	$36.48 - $54.51		$	40.65
	Outstanding at December 31, 2011	847,102		$17.34 - $60.23		$	39.93
	Granted	102,000		$58.95 - $58.95		$	58.95
	Exercised	(274,842	)	$17.34 - $57.16		$	34.04
	Canceled or expired	(541	)	$54.51 - $54.51		$	54.51
	Outstanding at December 31, 2012	673,719		$25.00 - $60.23		$	45.2
	Granted	126,800		$102.16 - $102.16		$	102.16
	Exercised	(409,799	)	$25.00 - $58.95		$	41.05
	Canceled or expired	(16,380	)	$36.48 - $58.95		$	47.54
	Outstanding at December 31, 2013	374,340		$36.48 - $102.16		$	68.94		7.34		$	43,289
	Exercisable at December 31, 2011	558,849		$17.34 - $55.07		$	37.15
	Exercisable at December 31, 2012	432,196		$25.00 - $60.23		$	40.22
	Exercisable at December 31, 2013	146,161		$36.48 - $60.23		$	47.72		5.44		$	20,004
	The aggregate intrinsic value is calculated as the difference between (i) the closing price of the common stock at December 31, 2011, 2012 and 2013 and (ii) the exercise prices of the underlying awards, multiplied by the shares underlying options as of December 31, 2011, 2012 and 2013, that had an exercise price less than the closing price on that date. Options to purchase 198,132, 274,842 and 409,799 shares were exercised for the years ended December 31, 2011, 2012, and 2013, respectively. The aggregate intrinsic value of options exercised, determined as of the date of option exercise, was $6.1 million, $11.9 million and $39.0 million for the years ended December 31, 2011, 2012, and 2013, respectively.
	At December 31, 2013, there was $38.6 million of unrecognized compensation cost related to stock-based payments, net of forfeitures, which is expected to be recognized over a weighted-average-period of 2.4 years. The $38.6 million of unrecognized compensation cost at December 31, 2013 included approximately $2.1 million of unrecognized compensation costs related to shares of restricted common stock that vest based on the achievement of Company performance conditions.
	The weighted-average grant date fair value of each option granted during the years ended December 31, 2011, 2012 and 2013 using the Black-Scholes option-pricing model was $21.57, $20.99 and $34.10 respectively.
	15	EMPLOYEE BENEFIT PLANS — (CONTINUED)
	Stock Incentive Plans — (Continued)
	The Company estimated the fair value of each option granted on the date of grant using the Black-Scholes option-pricing model, using the assumptions noted in the following table:
		Year Ended December 31,
		2011		2012			2013
	Dividend yield	0	%	0	%		0	%
	Expected volatility	40	%	40	%		37	%
	Risk-free interest rate	2.2	%	0.9	%		0.9	%
	Expected life (in years)	5		5			5
	The assumptions above and the estimation of expected forfeitures are based on multiple facts, including historical employee behavior patterns of exercising options and post-employment termination behavior, expected future employee option exercise patterns, and the historical volatility of the Company’s stock price.
	The following table summarizes information regarding options outstanding at December 31, 2013:
			Options Outstanding							Options Exercisable
	Range of		Number of		Weighted-Average Remaining Contractual Life (in years)		Weighted-			Number of			Weighted-
	Exercise Price		Shares				Average			Shares			Average
							Exercise Price						Exercise Price
	$36.48 - $41.21		16,991		4.94		$	37.84		16,991			$	37.84
	$41.22 - $42.50		45,900		6.19		$	42.29		45,900			$	42.29
	$42.51 - $53.22		38,296		2.33		$	46.14		36,037			$	46.35
	$53.23 - $55.83		4,054		6.92		$	54.51		3,243			$	54.51
	$55.84 - $57.61		61,198		7.17		$	57.16		28,930			$	57.16
	$57.62 - $58.51		745		7.09		$	58.06		—			$	—
	$58.52 - $59.59		78,036		8.14		$	58.95		13,900			$	58.95
	$59.60 - $81.19		2,320		7.42		$	60.23		1,160			$	60.23
	$81.20 - $102.16		126,800		9.19		$	102.16		—			$	—
	$36.48 - $102.16		374,340		7.34		$	68.94		146,161			$	47.72
	15	EMPLOYEE BENEFIT PLANS — (CONTINUED)
	Stock Incentive Plans — (Continued)
	The following table presents unvested restricted stock awards activity for the year ended December 31, 2013:
		Number of		Weighted-Average
		Shares		Grant Date
				Fair Value per Share
Unvested restricted stock at December 31, 2012	1,020,673		$	66.17
Granted	238,314		$	119.84
Vested	(206,248	)	$	58.64
Canceled	(84,469	)	$	71.51
Unvested restricted stock at December 31, 2013	968,270		$	80.52
Employee 401(k) Plan
The Company maintains a 401(k) Plan (the “401(k)”) as a defined contribution retirement plan for all eligible employees. The 401(k) provides for tax-deferred contributions of employees’ salaries, limited to a maximum annual amount as established by the Internal Revenue Service. In 2011 and 2012, the Company matched 50% of employee contributions up to a maximum of 6% of total compensation. In 2013, the Company matched 100% of employee contributions up to a maximum of 4% of total compensation. Amounts contributed to the 401(k) by the Company to match employee contributions for the years ended December 31, 2011, 2012 and 2013 were approximately $1.9 million, $2.7 million and $5.1 million, respectively. The Company had no administrative expenses in connection with the 401(k) plan for the years ended December 31, 2011, 2012 and 2013, respectively.
Employee Pension Plan
The Company maintains a company personal pension plan for all eligible employees in the Company’s U.K. offices. The plan is a defined contribution plan. Employees are eligible to contribute a portion of their salaries, subject to a maximum annual amount as established by Her Majesty's Revenue and Customs. In 2011 and 2012, the Company matched 50% of employee contributions up to a maximum of 6% of total compensation. In 2013, the Company's matching contribution was based on the percentage contributed by the employee, up to a maximum of 6% of total compensation. Amounts contributed to the plan by the Company to match employee contributions for the years ended December 31, 2011, 2012 and 2013 were approximately $160,000, $180,000 and $280,000, respectively.
Employee Stock Purchase Plan
As of August 1, 2006, the Company introduced an Employee Stock Purchase Plan (“ESPP”), pursuant to which eligible employees participating in the plan authorize the Company to withhold specified amounts from the employees’ compensation and use the withheld amounts to purchase shares of the Company's common stock at 90% of the market price. Participating employees are able to purchase common stock under this plan during each offering period. An offering period begins the second Saturday before each of the Company’s regular pay dates and ends on each of the Company’s regular pay dates. There were 46,186 and 34,895 shares available for purchase under the ESPP as of December 31, 2012 and 2013, respectively and approximately 10,153 and 11,291 shares of the Company’s common stock were purchased under the ESPP during 2012 and 2013, respectively.

Schedule_II_Valuation_and_Qual

Schedule II Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2013
Valuation and Qualifying Accounts [Abstract]	'
Schedule II - Valuation and Qualifying Accounts	'
	Schedule II – Valuation and Qualifying Accounts
	Years Ended December 31, 2011, 2012, and 2013 (in thousands):
	Allowance for doubtful accounts and billing adjustments (1)		Balance at		Charged to		Charged to		Write-offs,		Balance at
			Beginning		Expense		Other		Net of		End of Year
			of Year				Accounts (2)		Recoveries
	Year ended December 31, 2011		$	2,415	$	1,525	$	—	$	1,416	$	2,524
	Year ended December 31, 2012		$	2,524	$	1,456	$	475	$	1,520	$	2,935
	Year ended December 31, 2013		$	2,935	$	2,317	$	—	$	1,855	$	3,397
	(1)	Additions to the allowance for doubtful accounts are charged to bad debt expense.
	(2)	Amounts represent opening balances from acquired businesses.

SUMMARY_OF_SIGNIFICANT_ACCOUNT1

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Basis of Presentation	'
	Basis of Presentation
	The 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 U.S. generally accepted accounting principles (“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 consolidated statements of cash flows have been reclassified to conform to the Company’s current presentation.
Revenue Recognition	'
	Revenue Recognition
	The Company primarily derives revenues by providing access to its proprietary database of commercial real estate information. The Company generally charges a fixed monthly amount for its subscription-based services. Subscription contract rates are based on the number of sites, number of users, organization size, the client’s business focus, geography and the number of services to which a client subscribes. A majority of the subscription-based license agreements typically have a term of one year and renew automatically.
	Revenue is recognized when (1) there is persuasive evidence of an arrangement, (2) the fee is fixed and determinable, (3) services have been rendered and payment has been contractually earned and (4) collectability is reasonably assured.
	Revenues from subscription-based services are recognized on a straight-line basis over the term of the agreement. Deferred revenue results from advance cash receipts from customers or amounts billed in advance to customers from the sales of subscription licenses and is recognized over the term of the license agreement.
Cost of Revenues	'
	Cost of Revenues
	Cost of revenues principally consists of salaries and related expenses for the Company’s researchers who collect and analyze the commercial real estate data that is the basis for the Company’s information, analytics and marketing services. Additionally, cost of revenues includes the cost of data from third party data sources, credit card and other transaction fees relating to processing customer transactions, which are expensed as incurred, and the amortization of acquired trade names and database technology.
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 consolidated statements of operations. There were no material gains or losses from foreign currency exchange transactions for the years ended December 31, 2011, 2012 and 2013.
Accumulated Other Comprehensive Loss	'
	Accumulated Other Comprehensive Loss
	The components of accumulated other comprehensive loss were as follows (in thousands):
		Year Ended December 31,
		2012			2013
	Foreign currency translation adjustment	$	(4,613	)	$	(4,003	)
	Accumulated net unrealized loss on investments, net of tax	(1,905		)	(1,527		)
	Total accumulated other comprehensive loss	$	(6,518	)	$	(5,530	)
Advertising Costs	'
	Advertising Costs
	The Company expenses advertising costs as incurred. E-commerce advertising expenses were approximately $2.5 million, $4.4 million and $5.7 million for the years ended December 31, 2011, 2012 and 2013, respectively.
Income Taxes	'
	Income Taxes
	Deferred income taxes result from temporary differences between the tax basis of assets and liabilities and the basis reported in the Company’s consolidated financial statements. Deferred tax liabilities and assets are determined based on the difference between the financial statement and the tax basis of assets and liabilities using enacted rates expected to be in effect during the year in which the differences reverse. Valuation allowances are provided against assets, including net operating losses, if it is anticipated that some or all of an asset may not be realized through future taxable earnings or implementation of tax planning strategies. Interest and penalties related to income tax matters are recognized in income tax expense.
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 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, subject to certain approvals under the CoStar Group, Inc. 2007 Stock Incentive Plan. As of March 31, 2013, the Company initially determined that it was probable that the performance condition for these performance-based restricted common stock awards would be met by the March 31, 2017 forfeiture date. As of December 31, 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 $21.8 million of stock-based compensation expense related to performance-based restricted common stock for the year ended December 31, 2013. There was no stock-based compensation expense related to performance-based restricted common stock recorded for the years ended December 31, 2011 and December 31, 2012. The Company expects to record additional estimated unrecognized stock-based compensation expense related to performance-based restricted common stock of approximately $2.1 million 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.
Cash and Cash Equivalents	'
	Cash and Cash Equivalents
	The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. Cash equivalents consist of money market fund investments and commercial paper. As of December 31, 2012 and 2013, cash of approximately $0 and $105,000, respectively, was held to support letters of credit for security deposits.
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 consisted 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 were classified as current in the Company’s consolidated balance sheets because they represented 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 value.
Concentration of Credit Risk and Financial Instruments	'
	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. No single customer accounted for more than 5% of the Company’s revenues for each of the years ended December 31, 2011, 2012 and 2013. The carrying amount of the accounts receivable approximates the net realizable value. The carrying value of the accounts receivable, accounts payable, accrued expenses and long-term debt approximates fair value.
Accounts Receivable, Net of Allowance for Doubtful Accounts	'
	Accounts Receivable, Net of Allowance for Doubtful Accounts
	Accounts receivable are recorded at the invoiced amount. Accounts receivable payment terms vary and amounts due from customers are stated in the financial statements net of an allowance for doubtful accounts. The allowance for doubtful accounts is based on the Company’s assessment of the collectability of customer accounts. The Company regularly reviews the allowance by considering factors such as historical experience, the aging of the balances, and current economic conditions that may affect a customer’s ability to pay.
Property and Equipment	'
	Property and Equipment
	Property and equipment are stated at cost. All repairs and maintenance costs are expensed as incurred. Depreciation and amortization are calculated on a straight-line basis over the following estimated useful lives of the assets:
	Leasehold improvements		Shorter of lease term or useful life
	Furniture and office equipment		Five to ten years
	Research vehicles		Five years
	Computer hardware and software		Two to five years
	Qualifying internal-use software costs incurred during the application development stage, which consists primarily of outside services, purchased software license costs and internal product development costs are capitalized and amortized over the estimated useful life of the asset. All other costs are expensed as incurred.
Goodwill, Intangibles and Other Assets	'
	Goodwill, Intangibles and Other Assets
	Goodwill represents the excess of costs over the fair value of assets of acquired businesses. Goodwill and intangible assets acquired in a business combination and determined to have an indefinite useful life are not amortized, but instead tested for impairment at least annually by reporting unit. The Company’s operating segments, U.S. and International, are the reporting units tested for potential impairment. To determine whether it is necessary to perform the two-step goodwill impairment test, the Company may first assess qualitative factors to evaluate whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If the Company concludes that it is more likely than not that the fair value of a reporting unit is less than its carrying amount or if the Company elects not to assess qualitative factors, then the Company performs the two-step process. The first step is to determine the fair value of each reporting unit. The estimate of the fair value of each reporting unit is based on a projected discounted cash flow model that includes significant assumptions and estimates including the Company's discount rate, growth rate and future financial performance. Assumptions about the discount rate are based on a weighted average cost of capital for comparable companies. Assumptions about the growth rate and future financial performance of a reporting unit are based on the Company's forecasts, business plans, economic projections and anticipated future cash flows. The fair value of each reporting unit is compared to the carrying amount of the reporting unit. If the carrying value of the reporting unit exceeds the fair value, then the second step of the process is performed to measure the impairment loss. The impairment loss is measured based on a projected discounted cash flow method using a discount rate determined by the Company’s management to be commensurate with the risk in its current business model.
	To determine whether it is necessary to perform the quantitative impairment test for indefinite-lived intangible assets, the Company may first assess qualitative factors to evaluate whether it is more likely than not that the fair value of the indefinite-lived intangible assets is less than the carrying amount. If the Company concludes that it is more likely than not that the fair value of the indefinite-lived intangible assets is less than the carrying amount or if the Company elects not to assess qualitative factors, then the Company performs the quantitative impairment test similar to the test performed on goodwill discussed above.
	Intangible assets with estimable useful lives that arose from acquisitions on or after July 1, 2001 are amortized over their respective estimated useful lives using a method of amortization that reflects the pattern in which the economic benefits of the intangible assets are consumed or otherwise used up, and are reviewed at least annually for impairment.
	Acquired database technology, customer base and trade names and other are related to the Company’s acquisitions (see Notes 3, 7 and 8). With the exception of the acquired trade name recorded in connection with the acquisition of LoopNet, acquired database technology and trade names and other are amortized on a straight-line basis over periods ranging from two to ten years. The acquired trade name recorded in connection with the LoopNet acquisition has an indefinite estimated useful life and is not amortized, but is subject to annual impairment tests. The acquired intangible asset characterized as customer base consists of one distinct intangible asset composed of acquired customer contracts and the related customer relationships. Acquired customer bases are typically amortized on an accelerated basis related to the expected economic benefit of the intangible asset. The cost of capitalized building photography is amortized on a straight-line basis over five years.
Long-Lived Assets	'
	Long-Lived Assets
	Long-lived assets, such as property, plant, and equipment, and purchased intangibles subject to amortization, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to estimated undiscounted future cash flows expected to be generated by the asset or asset group. If the carrying amount of an asset exceeds its estimated future cash flows, an impairment charge is recognized in the amount by which the carrying amount of the asset exceeds the fair value of the asset.
	Assets to be disposed of would be separately presented in the balance sheet and reported at the lower of the carrying amount or fair value less costs to sell, and would no longer be depreciated. The assets and liabilities of a disposal group classified as held for sale would be presented separately in the appropriate asset and liability sections of the balance sheet.
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 $302,000 and $111,000 as of December 31, 2012 and 2013, respectively. These capitalized product development costs are included in intangible and other assets in the Company’s 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 $80,000, $191,000 and $191,000 for the years ended December 31, 2011, 2012 and 2013, respectively.
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 $9.6 million and $6.5 million as of December 31, 2012 and 2013, 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 9 for additional information regarding the financing commitment with J.P. Morgan Bank and the Credit Agreement. No amortization expense for debt issuance costs was recognized by the Company for the year ended December 31, 2011. The Company amortized debt issuance costs of approximately $2.0 million and $3.0 million for the years ended December 31, 2012 and 2013, respectively.
Recent Accounting Pronouncements	'
	Recent Accounting Pronouncements
	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, but the Company provided additional disclosures in its financial statements.
	There are no accounting pronouncements that have been recently issued but not yet adopted by the Company that would have a material impact on the Company’s results of operations or financial position.

SUMMARY_OF_SIGNIFICANT_ACCOUNT2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Schedule of accumulated other comprehensive loss	'
	The components of accumulated other comprehensive loss were as follows (in thousands):
		Year Ended December 31,
		2012			2013
	Foreign currency translation adjustment	$	(4,613	)	$	(4,003	)
	Accumulated net unrealized loss on investments, net of tax	(1,905		)	(1,527		)
	Total accumulated other comprehensive loss	$	(6,518	)	$	(5,530	)
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):
		Year Ended December 31,
		2011			2012			2013
	Cost of revenues	$	1,635		$	2,556		$	4,553
	Selling and marketing	1,339			1,966			4,954
	Software development	1,130			2,241			7,244
	General and administrative	3,999			5,519			24,798
	Total stock-based compensation	$	8,103		$	12,282		$	41,549
Property and equipment estimated useful lives	'
	Property and equipment are stated at cost. All repairs and maintenance costs are expensed as incurred. Depreciation and amortization are calculated on a straight-line basis over the following estimated useful lives of the assets:
	Leasehold improvements		Shorter of lease term or useful life
	Furniture and office equipment		Five to ten years
	Research vehicles		Five years
	Computer hardware and software		Two to five years

ACQUISITION_Tables

ACQUISITION (Tables) (LoopNet [Member])	12 Months Ended
	Dec. 31, 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)	12 Months Ended
	Dec. 31, 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 December 31, 2013 are as follows (in thousands):
	Maturity		Fair Value
	Due in:
	2014		$	—
	2015 — 2018		853
	2019 — 2023		—
	2024 and thereafter		21,137
	Available-for-sale investments		$	21,990
Schedule of available for sale securities reconciliation	'
	As of December 31, 2013, the amortized cost basis and fair value of investments classified as available-for-sale were as follows (in thousands):
		Amortized			Gross			Gross			Fair Value
		Cost			Unrealized			Unrealized
					Gains			Losses
	Auction rate securities	$	23,517		$	411		$	(1,938	)	$	21,990
	Available-for-sale investments	$	23,517		$	411		$	(1,938	)	$	21,990
	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 Value
		Cost			Unrealized			Unrealized
					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 more than twelve months were as follows (in thousands):
		December 31,
		2012						2013
		Aggregate			Gross			Aggregate			Gross
		Fair			Unrealized			Fair			Unrealized
		Value			Losses			Value			Losses
	Government-sponsored enterprise obligations	$	37		$	—		$	—		$	—
	Auction rate securities	21,119			(2,006		)	21,137			(1,938		)
	Investments in an unrealized loss position	$	21,156		$	(2,006	)	$	21,137		$	(1,938	)

FAIR_VALUE_Tables

FAIR VALUE (Tables)	12 Months Ended
	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'
Summary of fair value hierarchy for the company's 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 December 31, 2013 (in thousands):
		Level 1			Level 2		Level 3		Total
	Assets:
	Cash	$	134,989		$	—	$	—	$	134,989
	Money market funds	50,593			—		—		50,593
	Commercial paper	70,371			—		—		70,371
	Auction rate securities	—			—		21,990		21,990
	Total assets measured at fair value	$	255,953		$	—	$	21,990	$	277,943
	Liabilities:
	Deferred consideration	$	—		$	—	$	1,344	$	1,344
	Total liabilities measured at fair value	$	—		$	—	$	1,344	$	1,344
	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 table summarizes changes in fair value of the Company’s Level 3 assets from December 31, 2007 to December 31, 2013 (in thousands):
		Auction
		Rate
		Securities
	Balance at December 31, 2007	$	53,975
	Increase in unrealized loss included in accumulated other comprehensive loss	(3,710		)
	Settlements	(20,925		)
	Balance at December 31, 2008	29,340
	Decrease in unrealized loss included in accumulated other comprehensive loss	684
	Settlements	(300		)
	Balance at December 31, 2009	29,724
	Decrease in unrealized loss included in accumulated other comprehensive loss	40
	Settlements	(575		)
	Balance at December 31, 2010	29,189
	Decrease in unrealized loss included in accumulated other comprehensive loss	245
	Settlements	(4,850		)
	Balance at December 31, 2011	24,584
	Auction rate securities upon acquisition	442
	Decrease in unrealized loss included in accumulated other comprehensive loss	836
	Settlements	(4,200		)
	Balance at December 31, 2012	21,662
	Decrease in unrealized loss included in accumulated other comprehensive loss	378
	Settlements	(50		)
	Balance at December 31, 2013	$	21,990
Summary of changes in the fair value of the company's level 3 liabilities	'
	The following table summarizes changes in fair value of the Company’s Level 3 liabilities from December 31, 2011 to December 31, 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 for 2013	384
	Payments made in 2013	(1,344		)
	Balance at December 31, 2013	$	1,344

PROPERTY_AND_EQUIPMENT_Tables

PROPERTY AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2013
Property, Plant and Equipment [Abstract]	'
Schedule of property, plant and equipment	'
	Property and equipment consists of the following (in thousands):
		December 31,
		2012			2013
	Leasehold improvements	$	28,527		$	36,933
	Furniture, office equipment and research vehicles	25,837			27,395
	Computer hardware and software	36,688			36,391
		91,052			100,719
	Accumulated depreciation and amortization	(44,744		)	(43,000		)
	Property and equipment, net	$	46,308		$	57,719

GOODWILL_Tables

GOODWILL (Tables)	12 Months Ended
	Dec. 31, 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	—		509		509
	Goodwill, December 31, 2013	$	692,639	$	25,948	$	718,587

INTANGIBLES_AND_OTHER_ASSETS_T

INTANGIBLES AND OTHER ASSETS (Tables)	12 Months Ended
	Dec. 31, 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):
		December 31,						Weighted- Average
								Amortization Period
		2012			2013			(in years)
	Capitalized product development cost	$	2,140		$	2,140		4
	Accumulated amortization	(1,838		)	(2,029		)
	Capitalized product development cost, net	302			111
	Building photography	12,474			13,743			5
	Accumulated amortization	(11,639		)	(12,005		)
	Building photography, net	835			1,738
	Acquired database technology	77,328			77,368			5
	Accumulated amortization	(29,673		)	(41,073		)
	Acquired database technology, net	47,655			36,295
	Acquired customer base	130,683			130,960			10
	Accumulated amortization	(59,218		)	(74,734		)
	Acquired customer base, net	71,465			56,226
	Acquired trade names and other (1)	59,255			59,336			7
	Accumulated amortization	(8,880		)	(9,234		)
	Acquired trade names and other, net	50,375			50,102
	Intangibles and other assets, net	$	170,632		$	144,472
	(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_Tables

LONG-TERM DEBT (Tables)	12 Months Ended
	Dec. 31, 2013
Long-term Debt, Current and Noncurrent [Abstract]	'
Schedule of Maturities of Long-term Debt	'
	Maturities of the Company's borrowings under the Credit Agreement for each of the next four years as of December 31, 2013 are as follows (in thousands):
	Year ending December 31,	Maturities
	Due in:
	2014	$	24,063
	2015	32,812
	2016	61,250
	2017	35,000
	Long-term debt, including current maturities	$	153,125

INCOME_TAXES_Tables

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Schedule of components of income tax expense (benefit)	'
	The components of the provision (benefit) for income taxes attributable to operations consist of the following (in thousands):
		Year Ended December 31,
		2011			2012			2013
	Current:
	Federal	$	22,779		$	(2,260	)	$	26,516
	State	2,226			1,974			3,996
	Foreign	12			55			31
	Total current	25,017			(231		)	30,543
	Deferred:
	Federal	(14,661		)	15,512			(10,919		)
	State	(2,425		)	(2,067		)	(1,849		)
	Foreign	(18		)	5			28
	Total deferred	(17,104		)	13,450			(12,740		)
	Total provision for income taxes	$	7,913		$	13,219		$	17,803
Schedule of deferred tax assets and liabilities	'
	The components of deferred tax assets and liabilities consists of the following (in thousands):
		December 31,
		2012			2013
	Deferred tax assets:
	Reserve for bad debts	$	1,106		$	1,274
	Accrued compensation	4,830			6,725
	Stock compensation	4,946			13,381
	Net operating losses	20,431			17,457
	Accrued reserve and other	6,007			4,284
	Unrealized loss on securities	928			786
	Deferred rent	1,845			4,329
	Deferred revenue	1,220			1,538
	Deferred gain from sale of building	12,386			11,499
	Total deferred tax assets	53,699			61,273
	Deferred tax liabilities:
	Prepaids	(1,433		)	(1,096		)
	Depreciation	(3,676		)	(6,033		)
	Intangibles	(62,915		)	(55,284		)
	Total deferred tax liabilities	(68,024		)	(62,413		)
	Net deferred tax liabilities, prior to valuation allowance	(14,325		)	(1,140		)
	Valuation allowance	(10,490		)	(10,936		)
	Net deferred tax liabilities	$	(24,815	)	$	(12,076	)
Schedule of effective income tax rate reconciliation	'
	The Company’s provision for income taxes resulted in effective tax rates that varied from the statutory federal income tax rate as follows (in thousands):
		Year Ended December 31,
		2011			2012			2013
	Expected federal income tax provision at statutory rate	$	7,899		$	8,097		$	16,638
	State income taxes, net of federal benefit	(123		)	(1,360		)	885
	Foreign income taxes, net effect	(961		)	(2,971		)	(724		)
	Stock compensation	(143		)	(313		)	(116		)
	Increase in valuation allowance	643			2,978			588
	Nondeductible compensation	448			656			431
	Nondeductible transaction costs	—			5,829			—
	Other adjustments	150			303			101
	Income tax expense, net	$	7,913		$	13,219		$	17,803
Schedule of unrecognized tax benefits	'
	The following tables summarize the activity related to the Company’s unrecognized tax benefits (in thousands):
	Unrecognized tax benefit as of December 31, 2010	$	1,766
	Increase for current year tax positions	1,243
	Increase for prior year tax positions	445
	Expiration of the statute of limitation for assessment of taxes	(107		)
	Unrecognized tax benefit as of December 31, 2011	3,347
	Increase for current year tax positions	792
	Decrease for prior year tax positions	(161		)
	Expiration of the statute of limitation for assessment of taxes	(69		)
	Unrecognized tax benefit as of December 31, 2012	3,909
	Increase for current year tax positions	66
	Increase for prior year tax positions	2,037
	Expiration of the statute of limitation for assessment of taxes	(55		)
	Unrecognized tax benefit as of December 31, 2013	$	5,957

COMMITMENTS_AND_CONTINGENCIES_

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Future minimum lease payments	'
	Future minimum lease payments as of December 31, 2013 are as follows (in thousands):
	2014	$	17,004
	2015	15,128
	2016	14,104
	2017	14,317
	2018	13,916
	2019 and thereafter	69,475
	Total future minimum lease payments	$	143,944

SEGMENT_REPORTING_Tables

SEGMENT REPORTING (Tables)	12 Months Ended
	Dec. 31, 2013
Segment Reporting [Abstract]	'
Summarized information by operating segment	'
	Summarized information by operating segment was as follows (in thousands):
		Year Ended December 31,
		2011			2012			2013
	Revenues
	United States	$	233,381		$	330,805		$	420,817
	International
	External customers	18,357			19,131			20,126
	Intersegment revenue	1,140			1,514			339
	Total international revenue	19,497			20,645			20,465
	Intersegment eliminations	(1,140		)	(1,514		)	(339		)
	Total revenues	$	251,738		$	349,936		$	440,943
	EBITDA
	United States	$	38,099		$	70,199		$	97,348
	International	(3,476		)	(10,007		)	(3,136		)
	Total EBITDA	$	34,623		$	60,192		$	94,212
Reconciliation of EBITDA to net income	'
	Reconciliation of EBITDA to net income
	EBITDA	$	34,623		$	60,192		$	94,212
	Purchase amortization in cost of revenues	(1,353		)	(8,634		)	(11,883		)
	Purchase amortization in operating expenses	(2,237		)	(13,607		)	(15,183		)
	Depreciation and other amortization	(9,262		)	(10,511		)	(12,992		)
	Interest income	798			526			326
	Interest expense	—			(4,832		)	(6,943		)
	Income tax expense, net	(7,913		)	(13,219		)	(17,803		)
	Net income	$	14,656		$	9,915		$	29,734
Summarized information by operating segment, assets and liabilities	'
	Summarized information by operating segment consists of the following (in thousands):
		December 31,
		2012			2013
	Property and equipment, net
	United States	$	42,480		$	53,733
	International	3,828			3,986
	Total property and equipment, net	$	46,308		$	57,719
	Goodwill
	United States	$	692,639		$	692,639
	International	25,439			25,948
	Total goodwill	$	718,078		$	718,587
	Assets
	United States	$	1,215,949		$	1,311,292
	International	40,933			43,464
	Total operating segment assets	$	1,256,882		$	1,354,756
	Reconciliation of operating segment assets to total assets
	Total operating segment assets	$	1,256,882		$	1,354,756
	Investment in subsidiaries	(18,344		)	(18,344		)
	Intersegment receivables	(73,399		)	(79,430		)
	Total assets	$	1,165,139		$	1,256,982
	Liabilities
	United States	$	335,855		$	324,626
	International	70,108			79,266
	Total operating segment liabilities	$	405,963		$	403,892
	Reconciliation of operating segment liabilities to total liabilities
	Total operating segment liabilities	$	405,963		$	403,892
	Intersegment payables	(67,167		)	(74,772		)
	Total liabilities	$	338,796		$	329,120

NET_INCOME_PER_SHARE_Tables

NET INCOME PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2013
Earnings Per Share [Abstract]	'
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):
		Year Ended December 31,
		2011		2012		2013
	Numerator:
	Net income	$	14,656	$	9,915	$	29,734
	Denominator:
	Denominator for basic net income per share — weighted-average outstanding shares	23,131		26,533		27,670
	Effect of dilutive securities:
	Stock options and restricted stock	396		416		542
	Denominator for diluted net income per share — weighted-average outstanding shares	23,527		26,949		28,212
	Net income per share — basic	$	0.63	$	0.37	$	1.07
	Net income per share — diluted	$	0.62	$	0.37	$	1.05

EMPLOYEE_BENEFIT_PLANS_Tables

EMPLOYEE BENEFIT PLANS (Tables)	12 Months Ended
	Dec. 31, 2013
Compensation Related Costs [Abstract]	'
Schedule of option activity	'
	Option activity was as follows:
		Number of		Range of		Weighted-			Weighted-		Aggregate
		Shares		Exercise Price		Average			Average		Intrinsic
						Exercise			Remaining		Value
						Price			Contract		(in thousands)
									Life (in years)
	Outstanding at December 31, 2010	945,696		$17.34 - $55.07		$	36.1
	Granted	111,470		$57.16 - $60.23		$	57.28
	Exercised	(198,132	)	$17.97 - $54.51		$	31.37
	Canceled or expired	(11,932	)	$36.48 - $54.51		$	40.65
	Outstanding at December 31, 2011	847,102		$17.34 - $60.23		$	39.93
	Granted	102,000		$58.95 - $58.95		$	58.95
	Exercised	(274,842	)	$17.34 - $57.16		$	34.04
	Canceled or expired	(541	)	$54.51 - $54.51		$	54.51
	Outstanding at December 31, 2012	673,719		$25.00 - $60.23		$	45.2
	Granted	126,800		$102.16 - $102.16		$	102.16
	Exercised	(409,799	)	$25.00 - $58.95		$	41.05
	Canceled or expired	(16,380	)	$36.48 - $58.95		$	47.54
	Outstanding at December 31, 2013	374,340		$36.48 - $102.16		$	68.94		7.34		$	43,289
	Exercisable at December 31, 2011	558,849		$17.34 - $55.07		$	37.15
	Exercisable at December 31, 2012	432,196		$25.00 - $60.23		$	40.22
	Exercisable at December 31, 2013	146,161		$36.48 - $60.23		$	47.72		5.44		$	20,004
Fair value assumption for options granted	'
	The Company estimated the fair value of each option granted on the date of grant using the Black-Scholes option-pricing model, using the assumptions noted in the following table:
		Year Ended December 31,
		2011		2012			2013
	Dividend yield	0	%	0	%		0	%
	Expected volatility	40	%	40	%		37	%
	Risk-free interest rate	2.2	%	0.9	%		0.9	%
	Expected life (in years)	5		5			5
Summarized information regarding options outstanding	'
	The following table summarizes information regarding options outstanding at December 31, 2013:
			Options Outstanding							Options Exercisable
	Range of		Number of		Weighted-Average Remaining Contractual Life (in years)		Weighted-			Number of			Weighted-
	Exercise Price		Shares				Average			Shares			Average
							Exercise Price						Exercise Price
	$36.48 - $41.21		16,991		4.94		$	37.84		16,991			$	37.84
	$41.22 - $42.50		45,900		6.19		$	42.29		45,900			$	42.29
	$42.51 - $53.22		38,296		2.33		$	46.14		36,037			$	46.35
	$53.23 - $55.83		4,054		6.92		$	54.51		3,243			$	54.51
	$55.84 - $57.61		61,198		7.17		$	57.16		28,930			$	57.16
	$57.62 - $58.51		745		7.09		$	58.06		—			$	—
	$58.52 - $59.59		78,036		8.14		$	58.95		13,900			$	58.95
	$59.60 - $81.19		2,320		7.42		$	60.23		1,160			$	60.23
	$81.20 - $102.16		126,800		9.19		$	102.16		—			$	—
	$36.48 - $102.16		374,340		7.34		$	68.94		146,161			$	47.72
Unvested unrestricted stock awards activity	'
	The following table presents unvested restricted stock awards activity for the year ended December 31, 2013:
		Number of		Weighted-Average
		Shares		Grant Date
				Fair Value per Share
	Unvested restricted stock at December 31, 2012	1,020,673		$	66.17
	Granted	238,314		$	119.84
	Vested	(206,248	)	$	58.64
	Canceled	(84,469	)	$	71.51
	Unvested restricted stock at December 31, 2013	968,270		$	80.52

Schedule_II_Valuation_and_Qual1

Schedule II Valuation and Qualifying Accounts (Tables)	12 Months Ended
	Dec. 31, 2013
Valuation and Qualifying Accounts [Abstract]	'
Allowance for doubtful accounts and billing adjustments	'
	Years Ended December 31, 2011, 2012, and 2013 (in thousands):
	Allowance for doubtful accounts and billing adjustments (1)		Balance at		Charged to		Charged to		Write-offs,		Balance at
			Beginning		Expense		Other		Net of		End of Year
			of Year				Accounts (2)		Recoveries
	Year ended December 31, 2011		$	2,415	$	1,525	$	—	$	1,416	$	2,524
	Year ended December 31, 2012		$	2,524	$	1,456	$	475	$	1,520	$	2,935
	Year ended December 31, 2013		$	2,935	$	2,317	$	—	$	1,855	$	3,397
	(1)	Additions to the allowance for doubtful accounts are charged to bad debt expense.
	(2)	Amounts represent opening balances from acquired businesses.

ORGANIZATION_Details

ORGANIZATION (Details)	12 Months Ended
	Dec. 31, 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 (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Summary of Significant Accounting Policies [Line Items]	'	'	'
Term of subscription-based license agreements (in years)	'1 year	'	'
Material gains or losses from foreign currency exchange transactions	$0	$0	$0
Reclassifications out of accumulated other comprehensive loss	0	0	0
Advertising costs	5,700,000	4,400,000	2,500,000
Maximum original maturity of highly liquid investments to be considered cash equivalents (in months)	'3 months	'	'
Cash held to support letters of credit for security deposits	105,000	0	'
Short-term investment maturities (in days)	'90 days	'	'
Available for sale short term investment contractual maturities (in years)	'1 year	'	'
Number of customers accouting for more than 5% of revenue (in customers)	0	0	0
Significant customer revenue threshold percent	5.00%	5.00%	5.00%
Amortization expense for capitalized product development costs	15,183,000	13,607,000	2,237,000
Capitalized product development costs, net	144,472,000	170,632,000	'
Capitalized debt issuance costs	6,542,000	9,556,000	'
Amortization of debt issuance costs	3,014,000	1,989,000	0
Minimum [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Short-term investment maturities (in days)	'90 days	'	'
Available for sale short term investment contractual maturities (in years)	'1 year	'	'
Building [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Property and equipment, estimated useful life (in years)	'39 years	'	'
Furniture and Office Equipment [Member] | Minimum [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Property and equipment, estimated useful life (in years)	'5 years	'	'
Furniture and Office Equipment [Member] | Maximum [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Property and equipment, estimated useful life (in years)	'10 years	'	'
Vehicles [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Property and equipment, estimated useful life (in years)	'5 years	'	'
Computer Hardware and Software [Member] | Minimum [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Property and equipment, estimated useful life (in years)	'2 years	'	'
Computer Hardware and Software [Member] | Maximum [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Property and equipment, estimated useful life (in years)	'5 years	'	'
Acquired Database Technology [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Capitalized product development costs, net	36,295,000	47,655,000	'
Acquired Database Technology [Member] | Minimum [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Finite-lived intangible asset, useful life (in years)	'2 years	'	'
Acquired Database Technology [Member] | Maximum [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Finite-lived intangible asset, useful life (in years)	'10 years	'	'
Acquired Trade Names and Other [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Capitalized product development costs, net	50,102,000	50,375,000	'
Acquired Trade Names and Other [Member] | Minimum [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Finite-lived intangible asset, useful life (in years)	'2 years	'	'
Acquired Trade Names and Other [Member] | Maximum [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Finite-lived intangible asset, useful life (in years)	'10 years	'	'
Acquired Customer Base [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Number of distinct intangible asset	1	'	'
Capitalized product development costs, net	56,226,000	71,465,000	'
Building Photography [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Finite-lived intangible asset, useful life (in years)	'5 years	'	'
Capitalized product development costs, net	1,738,000	835,000	'
Capitalized Product Development Costs [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Amortization expense for capitalized product development costs	191,000	191,000	80,000
Capitalized product development costs, net	$111,000	$302,000	'
Capitalized Product Development Costs [Member] | Minimum [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Finite-lived intangible asset, useful life (in years)	'3 years	'	'
Capitalized Product Development Costs [Member] | Maximum [Member]	'	'	'
Summary of Significant Accounting Policies [Line Items]	'	'	'
Finite-lived intangible asset, useful life (in years)	'5 years	'	'

SUMMARY_OF_SIGNIFICANT_ACCOUNT4

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS), NET OF TAX (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Accumulated Other Comprehensive Income (Loss) Net of Tax [Abstract]	'	'
Foreign currency translation adjustment	($4,003)	($4,613)
Accumulated net unrealized loss on investments, net of tax	-1,527	-1,905
Total accumulated other comprehensive loss	($5,530)	($6,518)

SUMMARY_OF_SIGNIFICANT_ACCOUNT5

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, STOCK BASED COMPENSATION EXPENSE (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Stock-Based Compensation Expense [Abstract]	'	'	'
Compensation expense	$41,549,000	$12,282,000	$8,103,000
Net cash proceeds from the exercise of stock options and ESPP	18,133,000	9,868,000	6,622,000
Excess tax benefit from stock-based compensation	19,585,000	198,000	2,541,000
Cost of revenues	'	'	'
Stock-Based Compensation Expense [Abstract]	'	'	'
Compensation expense	4,553,000	2,556,000	1,635,000
Selling and marketing	'	'	'
Stock-Based Compensation Expense [Abstract]	'	'	'
Compensation expense	4,954,000	1,966,000	1,339,000
Software development	'	'	'
Stock-Based Compensation Expense [Abstract]	'	'	'
Compensation expense	7,244,000	2,241,000	1,130,000
General and administrative	'	'	'
Stock-Based Compensation Expense [Abstract]	'	'	'
Compensation expense	24,798,000	5,519,000	3,999,000
Performance-Based Restricted Common Stock [Member]	'	'	'
Stock-Based Compensation Expense [Abstract]	'	'	'
Compensation expense	21,752,000	0	0
Unrecognized compensation cost expected to be recognized in future years	$2,100,000	'	'

ACQUISITION_Details

ACQUISITION (Details) (USD $)	Apr. 26, 2012	3-May-12	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Apr. 30, 2012	Dec. 31, 2013	Apr. 30, 2012	Dec. 31, 2013	Apr. 30, 2012
		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	distinct_intangible_asset	LoopNet [Member]		LoopNet [Member]
Business Acquisition [Line Items]	'	'	'	'	'	'	'	'	'	'
Percentage of outstanding stock controlled by company	'	'	'	'	'	100.00%	'	'	'	'
Number of distinct intangible asset	'	'	'	'	'	1	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	5,200,000	14,200,000	'	'	'	'	'
Term of consent order public comment period	'30 days	'	'	'	'	'	'	'	'	'
Proceeds from sale of Xcelignet	'	4,200,000	'	'	'	'	'	'	'	'
Gain on sale of Xceligent	'	$0	'	'	'	'	'	'	'	'

ACQUISITION_Schedule_of_Consid

ACQUISITION (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 (1,880,300 shares at $72.89)	137,055
Fair value of total consideration transferred	$883,448

ACQUISITION_Schedule_of_Assets

ACQUISITION (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 $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]	'	'
Short-term investment maturities (in days)	'90 days	'
Available for sale short term investment contractual maturities (in years)	'1 year	'
Debt Maturities Fair Value [Abstract]	'	'
2014	$0	'
2015 — 2018	853	'
2019 — 2023	0	'
2024 and thereafter	21,137	'
Available-for-sale investments	$21,990	$21,699
Minimum [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
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 $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
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, Gross Realized Gains	0	0	0
Available-for-sale Securities, Gross Realized Losses	0	0	0
Available-for-sale Securities Reconciliation [Abstract]	'	'	'
Amortized Cost	23,517,000	23,604,000	'
Gross Unrealized Gains	411,000	101,000	'
Gross Unrealized Losses	-1,938,000	-2,006,000	'
Available-for-sale investments	21,990,000	21,699,000	'
Available-for-sale securities, unrealized loss positions	'	'	'
Aggregate Fair Value	21,137,000	21,156,000	'
Government-Sponsored Enterprise Obligations [Member]	'	'	'
Available-for-sale Securities Reconciliation [Abstract]	'	'	'
Amortized Cost	'	37,000	'
Gross Unrealized Gains	'	0	'
Gross Unrealized Losses	0	0	'
Available-for-sale investments	'	37,000	'
Available-for-sale securities, unrealized loss positions	'	'	'
Aggregate Fair Value	0	37,000	'
Auction Rate Securities [Member]	'	'	'
Available-for-sale Securities Reconciliation [Abstract]	'	'	'
Amortized Cost	23,517,000	23,567,000	'
Gross Unrealized Gains	411,000	101,000	'
Gross Unrealized Losses	-1,938,000	-2,006,000	'
Available-for-sale investments	21,990,000	21,662,000	'
Available-for-sale securities, unrealized loss positions	'	'	'
Aggregate Fair Value	$21,137,000	$21,119,000	'

FAIR_VALUE_Details

FAIR VALUE (Details) (USD $)

12 Months Ended

12 Months Ended

12 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2009

Dec. 31, 2008

Dec. 31, 2013

Mar. 28, 2013

Dec. 31, 2013

Mar. 28, 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]

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

'

'

$277,943,000

$177,726,000

$134,989,000

$135,232,000

$50,593,000

$20,775,000

$70,371,000

$20,000

$37,000

$21,990,000

$21,662,000

$255,953,000

$156,027,000

$134,989,000

$135,232,000

$50,593,000

$20,775,000

$70,371,000

$20,000

$0

$0

$0

$0

$37,000

$0

$0

$0

$0

$0

$0

$37,000

$0

$0

$21,990,000

$21,662,000

$0

$0

$0

$0

$0

$0

$0

$21,990,000

$21,662,000

'

'

'

'

'

'

'

'

'

'

'

Unobservable inputs assets (level 3) [Roll forward]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Beginning balance

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

21,662,000

24,584,000

29,189,000

29,724,000

29,340,000

53,975,000

'

'

'

'

'

Auction rate securities upon acquisition

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

442,000

'

'

'

'

'

'

'

'

'

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

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

378,000

836,000

245,000

40,000

684,000

-3,710,000

'

'

'

'

'

Settlements

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-50,000

-4,200,000

-4,850,000

-575,000

-300,000

-20,925,000

'

'

'

'

'

Ending balance

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

21,990,000

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 the underlying securities involved in the auction rate securities (in years)

'20 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Par value of company held auction rate securities

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

24,300,000

'

'

'

'

'

'

'

'

'

'

Temporary impairment of the auction rates security investments

-1,527,000

-1,905,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-1,527,000

'

'

'

'

'

'

'

'

'

'

Liabilities:

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Deferred consideration

'

'

1,344,000

2,304,000

'

'

'

'

'

'

'

'

'

0

0

'

'

'

'

'

'

'

'

'

0

0

'

'

'

'

'

'

'

'

'

1,344,000

2,304,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unobservable inputs liabilities (level 3) [Roll forward]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Beginning balance

2,304,000

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Accretion

384,000

293,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Deferred consideration upon acquisition

'

2,011,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Payments

-1,344,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Ending balance

1,344,000

2,304,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Business acquisition deferred consideration potential cash payment (undiscounted)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,000,000

'

344,000

'

'

Discount rate (in percent)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4.90%

5.10%

'

'

'

'

'

'

'

'

23.50%

Business acquisition deferred consideration cash payment

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$1,000,000

'

$344,000

'

PROPERTY_AND_EQUIPMENT_Details

PROPERTY AND EQUIPMENT (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]	'	'	'
Property and equipment, gross	$100,719	$91,052	'
Accumulated depreciation and amortization	-43,000	-44,744	'
Property and equipment, net	57,719	46,308	'
Depreciation expense for property and equipment	12,495	10,053	8,435
Leasehold Improvements [Member]	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'
Property and equipment, gross	36,933	28,527	'
Furniture, Office Equipment and Research Vehicles [Member]	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'
Property and equipment, gross	27,395	25,837	'
Computer Hardware and Software [Member]	'	'	'
Property, Plant and Equipment [Line Items]	'	'	'
Property and equipment, gross	$36,391	$36,688	'

GOODWILL_Details

GOODWILL (Details) (USD $)	12 Months Ended		0 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Apr. 30, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2012
			LoopNet [Member]	United States [Member]	United States [Member]	International [Member]	International [Member]
Goodwill [Line Items]	'	'	'	'	'	'	'
Goodwill, period increase (decrease)	'	'	$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	509	1,120	'	0	0	509	1,120
Goodwill, ending balance	$718,587	$718,078	'	$692,639	$692,639	$25,948	$25,439

INTANGIBLES_AND_OTHER_ASSETS_D

INTANGIBLES AND OTHER ASSETS (Details) (USD $)

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

0 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Apr. 30, 2012

Apr. 30, 2012

Apr. 30, 2012

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]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Finite-lived intangible assets, gross

'

'

'

$2,140,000

$2,140,000

$13,743,000

$12,474,000

$77,368,000

$77,328,000

$130,960,000

$130,683,000

$59,336,000

$59,255,000

'

'

'

Finite-lived intangible assets, accumulated amortization

'

'

'

-2,029,000

-1,838,000

-12,005,000

-11,639,000

-41,073,000

-29,673,000

-74,734,000

-59,218,000

-9,234,000

-8,880,000

'

'

'

Finite-lived intangible assets, net

144,472,000

170,632,000

'

111,000

302,000

1,738,000

835,000

36,295,000

47,655,000

56,226,000

71,465,000

50,102,000

50,375,000

'

'

'

Weighted-average amortization period (in years}

'

'

'

'4 years

'

'5 years

'

'5 years

'

'10 years

'

'7 years

'

'

'5 years

'10 years

Acquired trade names and other

'

'

'

'

'

'

'

'

'

'

'

'

'

48,700,000

'

'

Amortization of Intangible Assets

27,563,000

22,699,000

4,417,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Amortization expense for 2014

23,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Amortization expense for 2015

20,800,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Amortization expense for 2016

18,900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Amortization expense for 2017

10,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Amortization expense for 2018

$5,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

LONGTERM_DEBT_Details

LONG-TERM DEBT (Details) (USD $)

0 Months Ended

12 Months Ended

27 Months Ended

12 Months Ended

0 Months Ended

0 Months Ended

0 Months Ended

Feb. 16, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

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

Feb. 16, 2012

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]

Federal Funds Rate [Member]

LIBOR [Member]

LoopNet [Member]

LoopNet [Member]

LoopNet [Member]

LoopNet [Member]

CoStar Group [Member]

CoStar Group [Member]

Committed Term Loan [Member]

New Term Loan [Member]

New Term Loan [Member]

New Revolving Credit Facility [Member]

Swingline Loan [Member]

Letter of Credit [Member]

Business Acquisition [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt instrument borrowing capacity

'

'

'

'

'

'

'

'

'

$175,000,000

'

$50,000,000

'

'

'

'

'

'

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

'

'

'

'

'

'

'

'

'

'

'

'

'

'

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)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.50%

2.00%

LIBOR period (in months)

'1 month

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Basis spread on variable rate, one month interest period (in percent)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1.00%

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 (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

50.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

First excess cash flow repayment requirement (in percent)

'

'

'

'

'

'

'

'

'

'

'

'

300.00%

'

'

'

'

'

Second excess cash flow repayment requirement (in percent)

'

'

'

'

'

'

'

'

'

'

'

'

250.00%

300.00%

'

'

'

'

Second excess cash flow repayment percentage

25.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Third excess cash flow repayment requirement (in percent)

'

'

'

'

'

'

'

'

'

'

'

'

'

250.00%

'

'

'

'

Third excess cash flow repayment percentage

0.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unamortized debt issuance expense

'

11,500,000

'

'

11,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt issuance underwriting fees

'

'

'

'

9,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Legal fees associated with the debt issuance

'

'

'

'

2,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt interest expense

'

'

'

'

'

6,943,000

4,832,000

0

'

'

'

'

'

'

'

'

'

'

Amortization of debt issuance costs

'

3,014,000

1,989,000

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest paid

'

$4,291,000

$2,480,000

$0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

LONGTERM_DEBT_Schedule_of_Matu

LONG-TERM DEBT (Schedule of Maturities of Long-Term Debt) (Details) (USD $)	Dec. 31, 2013
In Thousands, unless otherwise specified
Long-term Debt, Current and Noncurrent [Abstract]	'
2014	$24,063
2015	32,812
2016	61,250
2017	35,000
Long-term debt, including current maturities	$153,125

INCOME_TAXES_Details

INCOME TAXES (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current:	'	'	'
Federal	$26,516,000	($2,260,000)	$22,779,000
State	3,996,000	1,974,000	2,226,000
Foreign	31,000	55,000	12,000
Total current	30,543,000	-231,000	25,017,000
Deferred:	'	'	'
Federal	-10,919,000	15,512,000	-14,661,000
State	-1,849,000	-2,067,000	-2,425,000
Foreign	28,000	5,000	-18,000
Total deferred	-12,740,000	13,450,000	-17,104,000
Total provision for income taxes	17,803,000	13,219,000	7,913,000
Deferred tax assets:	'	'	'
Reserve for bad debts	1,274,000	1,106,000	'
Accrued compensation	6,725,000	4,830,000	'
Stock compensation	13,381,000	4,946,000	'
Net operating losses	17,457,000	20,431,000	'
Accrued reserve and other	4,284,000	6,007,000	'
Unrealized loss on securities	786,000	928,000	'
Deferred rent	4,329,000	1,845,000	'
Deferred revenue	1,538,000	1,220,000	'
Deferred gain from sale of building	11,499,000	12,386,000	'
Total deferred tax assets	61,273,000	53,699,000	'
Deferred tax liabilities:	'	'	'
Prepaids	-1,096,000	-1,433,000	'
Depreciation	-6,033,000	-3,676,000	'
Intangibles	-55,284,000	-62,915,000	'
Total deferred tax liabilities	-62,413,000	-68,024,000	'
Net deferred tax liabilities, prior to valuation allowance	-1,140,000	-14,325,000	'
Valuation allowance	-10,936,000	-10,490,000	'
Net deferred tax liabilities	-12,076,000	-24,815,000	'
Income from U.S. sources	53,200,000	36,100,000	29,100,000
Loss from foreign sources	-5,600,000	-13,000,000	-6,600,000
Effective tax rate reconciliation [Abstract]	'	'	'
Expected federal income tax provision at statutory rate	16,638,000	8,097,000	7,899,000
State income taxes, net of federal benefit	885,000	-1,360,000	-123,000
Foreign income taxes, net effect	-724,000	-2,971,000	-961,000
Stock compensation	-116,000	-313,000	-143,000
Increase in valuation allowance	588,000	2,978,000	643,000
Nondeductible compensation	431,000	656,000	448,000
Nondeductible transaction costs	0	5,829,000	0
Other adjustments	101,000	303,000	150,000
Total provision for income taxes	17,803,000	13,219,000	7,913,000
Income taxes paid	6,500,000	2,600,000	19,500,000
Operating Loss Carryforwards [Line Items]	'	'	'
Change in valuation allowance	-446,000	-5,220,000	'
Cash tax benefits resulting in net operating loss carryforward	4,200,000	12,200,000	'
Unrecognized Tax Benefits [Roll Forward]	'	'	'
Unrecognized tax benefit beginning balance	3,909,000	3,347,000	1,766,000
Increase for current year tax positions	66,000	792,000	1,243,000
Decrease for prior period tax positions	'	-161,000	'
Increase for prior year tax positions	2,037,000	'	445,000
Expiration of the statute of limitation for assessment of taxes	-55,000	-69,000	-107,000
Unrecognized tax benefit ending balance	5,957,000	3,909,000	3,347,000
Unrecognized tax benefit that would favorably affect the annual effective tax rate if recognized in future periods	1,600,000	1,600,000	'
Interest and penalties on income taxes recognized	62,000	58,000	39,000
Interest and penalties accrued on income taxes	404,000	342,000	284,000
Foreign Country [Member]	'	'	'
Operating Loss Carryforwards [Line Items]	'	'	'
Change in valuation allowance	-765,000	'	'
Net operating loss carryforward	31,200,000	'	'
Domestic Country [Member]	'	'	'
Operating Loss Carryforwards [Line Items]	'	'	'
Net operating loss carryforward	13,500,000	'	'
Operating loss carryforwards, first expiration date	31-Dec-20	'	'
State and Local Jurisdiction [Member]	'	'	'
Operating Loss Carryforwards [Line Items]	'	'	'
Change in valuation allowance	-319,000	'	'
Net operating loss carryforward	4,900,000	'	'
Operating loss carryforwards, first expiration date	31-Dec-20	'	'
Income tax credit carryforward	$1,800,000	'	'

COMMITMENTS_AND_CONTINGENCIES_1

COMMITMENTS AND CONTINGENCIES (Details) (USD $)	1 Months Ended	12 Months Ended					0 Months Ended
	31-May-11	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2013	Feb. 16, 2012	Feb. 16, 2012
	class_action_lawsuits	current_litigation_matters			LoopNet Stockholders [Member]	Civix [Member]	LoopNet [Member]	LoopNet [Member]
							CoStar Group [Member]	CoStar Group [Member]
							New Term Loan [Member]	New Revolving Credit Facility [Member]
Operating Leases Rent Expense [Abstract]	'	'	'	'	'	'	'	'
Rent expense for operating leases	'	$18,300,000	$16,700,000	$13,300,000	'	'	'	'
Future Minimum Lease Payments [Abstract]	'	'	'	'	'	'	'	'
2014	'	17,004,000	'	'	'	'	'	'
2015	'	15,128,000	'	'	'	'	'	'
2016	'	14,104,000	'	'	'	'	'	'
2017	'	14,317,000	'	'	'	'	'	'
2018	'	13,916,000	'	'	'	'	'	'
2019 and thereafter	'	69,475,000	'	'	'	'	'	'
Total future minimum lease payments	'	143,944,000	'	'	'	'	'	'
Business Acquisition [Line Items]	'	'	'	'	'	'	'	'
Debt instrument borrowing capacity	'	'	'	'	'	'	175,000,000	50,000,000
Term of loan (in years)	'	'	'	'	'	'	'5 years	'5 years
Number of class action lawsuits brought by alleged LoopNet stockholders	3	'	'	'	'	'	'	'
Loss contingency accrual	'	'	'	'	200,000	600,000	'	'
Loss contingency, estimated damages sought	'	3,700,000	'	'	'	'	'	'
Estimate of possible loss in excess of amount accrued	'	'	'	'	'	$3,100,000	'	'
Number of minimum of current litigation matters (in claims)	'	1	'	'	'	'	'	'

SEGMENT_REPORTING_Details

SEGMENT REPORTING (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	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	$440,943,000	$349,936,000	$251,738,000
Property and equipment, net	57,719,000	46,308,000	'
Goodwill	718,587,000	718,078,000	91,784,000
Reconciliation of EBITDA to net income [Abstract]	'	'	'
EBITDA	94,212,000	60,192,000	34,623,000
Purchase amortization in cost of revenues	-11,883,000	-8,634,000	-1,353,000
Purchase amortization in operating expenses	-15,183,000	-13,607,000	-2,237,000
Depreciation and other amortization	-12,992,000	-10,511,000	-9,262,000
Interest income	326,000	526,000	798,000
Interest expense	-6,943,000	-4,832,000	0
Income tax expense, net	-17,803,000	-13,219,000	-7,913,000
Net income	29,734,000	9,915,000	14,656,000
Reconciliation of operating segment assets to total assets [Abstract]	'	'	'
Total operating segment assets	1,354,756,000	1,256,882,000	'
Investment in subsidiaries	-18,344,000	-18,344,000	'
Intersegment receivables	-79,430,000	-73,399,000	'
Total assets	1,256,982,000	1,165,139,000	'
Reconciliation of operating segment liabilities to total liabilities [Abstract]	'	'	'
Total operating segment liabilities	403,892,000	405,963,000	'
Intersegment payables	-74,772,000	-67,167,000	'
Total liabilities	329,120,000	338,796,000	'
United States [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Corporate allocation US	800,000	0	0
Summarized information by operating segment [Abstract]	'	'	'
Revenues	420,817,000	330,805,000	233,381,000
Property and equipment, net	53,733,000	42,480,000	'
Goodwill	692,639,000	692,639,000	67,465,000
Reconciliation of EBITDA to net income [Abstract]	'	'	'
EBITDA	97,348,000	70,199,000	38,099,000
Reconciliation of operating segment assets to total assets [Abstract]	'	'	'
Total operating segment assets	1,311,292,000	1,215,949,000	'
Reconciliation of operating segment liabilities to total liabilities [Abstract]	'	'	'
Total operating segment liabilities	324,626,000	335,855,000	'
International [Member]	'	'	'
Segment Reporting Information [Line Items]	'	'	'
Corporate allocation	400,000	5,300,000	800,000
Summarized information by operating segment [Abstract]	'	'	'
Revenues	20,465,000	20,645,000	19,497,000
Property and equipment, net	3,986,000	3,828,000	'
Goodwill	25,948,000	25,439,000	24,319,000
Reconciliation of EBITDA to net income [Abstract]	'	'	'
EBITDA	-3,136,000	-10,007,000	-3,476,000
Reconciliation of operating segment assets to total assets [Abstract]	'	'	'
Total operating segment assets	43,464,000	40,933,000	'
Reconciliation of operating segment liabilities to total liabilities [Abstract]	'	'	'
Total operating segment liabilities	79,266,000	70,108,000	'
External Customers [Member]	'	'	'
Summarized information by operating segment [Abstract]	'	'	'
Revenues	20,126,000	19,131,000	18,357,000
Intersegment Revenue [Member]	'	'	'
Summarized information by operating segment [Abstract]	'	'	'
Revenues	339,000	1,514,000	1,140,000
Intersegment Elimination [Member]	'	'	'
Summarized information by operating segment [Abstract]	'	'	'
Revenues	($339,000)	($1,514,000)	($1,140,000)

STOCKHOLDERS_EQUITY_Details

STOCKHOLDERS' EQUITY (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Jun. 05, 2012
Preferred stock	'	'	'
Preferred stock authorized for issuance (in shares)	2,000,000	2,000,000	'
Preferred stock, par value (in dollars per share)	$0.01	$0.01	'
Common stock	'	'	'
Common stock authorized for issuance (in shares)	60,000,000	60,000,000	'
Common stock par value (in dollars per share)	$0.01	$0.01	'
Increase in shares authorized (in shares)	'	'	30,000,000

NET_INCOME_PER_SHARE_Details

NET INCOME PER SHARE (Details) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Numerator:	'	'	'
Net income	$29,734	$9,915	$14,656
Denominator:	'	'	'
Denominator for basic net income per share — weighted-average outstanding shares	27,670,000	26,533,000	23,131,000
Effect of dilutive securities:	'	'	'
Stock options and restricted stock (in shares)	542,000	416,000	396,000
Denominator for diluted net income per share — weighted-average outstanding shares	28,212,000	26,949,000	23,527,000
Net income per share — basic (in dollars per share)	$1.07	$0.37	$0.63
Net income per share — diluted (in dollars per share)	$1.05	$0.37	$0.62
Stock Options [Member]	'	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'
Antidilutive securities excluded from computation of earnings per share (in shares)	0	0	2,300

EMPLOYEE_BENEFIT_PLANS_Details

EMPLOYEE BENEFIT PLANS (Details) (USD $)

12 Months Ended

0 Months Ended

12 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Jun. 05, 2012

Jun. 02, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Employee 401(k) Plan [Member]

Employee 401(k) Plan [Member]

Employee 401(k) Plan [Member]

Employee Pension Plan, London Office [Member]

Employee Pension Plan, London Office [Member]

Employee Pension Plan, London Office [Member]

Options Outstanding 1 [Member]

Options Outstanding 2 [Member]

Options Outstanding 3 [Member]

Options Outstanding 4 [Member]

Options Outstanding 5 [Member]

Options Outstanding 6 [Member]

Options Outstanding 7 [Member]

Options Outstanding 8 [Member]

Options Outstanding 9 [Member]

Options Outstanding 10 [Member]

Options Exercisable 1 [Member]

Options Exercisable 2 [Member]

Options Exercisable 3 [Member]

Options Exercisable 4 [Member]

Options Exercisable 5 [Member]

Options Exercisable 6 [Member]

Options Exercisable 7 [Member]

Options Exercisable 8 [Member]

Options Exercisable 9 [Member]

Options Exercisable 10 [Member]

1998 Stock Incentive Plan [Member]

CoStar Group, Inc. 2007 Stock Incentive Plan [Member]

CoStar Group, Inc. 2007 Stock Incentive Plan [Member]

CoStar Group, Inc. 2007 Stock Incentive Plan [Member]

CoStar Group, Inc. 2007 Stock Incentive Plan [Member]

Employee Stock Purchase Plan [Member]

Employee Stock Purchase Plan [Member]

Stock Options [Member]

Stock Options [Member]

Stock Options [Member]

Restricted Stock [Member]

Performance-Based Restricted Common Stock [Member]

Performance-Based Restricted Common Stock [Member]

Performance-Based Restricted Common Stock [Member]

Minimum [Member]

Minimum [Member]

Minimum [Member]

Minimum [Member]

Minimum [Member]

Minimum [Member]

Maximum [Member]

Maximum [Member]

Maximum [Member]

Maximum [Member]

Maximum [Member]

quarters

1998 Stock Incentive Plan [Member]

CoStar Group, Inc. 2007 Stock Incentive Plan [Member]

Stock Options [Member]

Stock Options [Member]

Stock Options [Member]

Restricted Stock [Member]

1998 Stock Incentive Plan [Member]

CoStar Group, Inc. 2007 Stock Incentive Plan [Member]

Stock Options [Member]

Stock Options [Member]

Stock Options [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Shares available for future grant under the plan (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

'

'

1,200,000

1,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Vesting period of options and restricted stock grants

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'3 years

'3 years

'

'

'

'1 year

'4 years

'4 years

'

'

'

Increase in shares of common stock pursuant to amendment to the plan (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Increase in shares of common stock issued pursuant to stock plan (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Shares of common stock authorized for issuance under the plan (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

121,875

'

'

3,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Cumulative EBITDA required for award shares to vest

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$90,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of consecutive quarters to mantain cumulative EBITDA required for award shares to vest (in quarters)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4

'

'

'

'

'

'

'

'

'

'

'

'

'

Compensation expense

41,549,000

12,282,000

8,103,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

21,752,000

0

0

'

'

'

'

'

'

'

'

'

'

'

Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding at beginning of period (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

673,719

847,102

945,696

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Granted (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

126,800

102,000

111,470

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exercised (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-409,799

-274,842

-198,132

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Canceled or expired (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-16,380

-541

-11,932

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding at end of period (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

374,340

673,719

847,102

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exercisable at end of period (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

146,161

432,196

558,849

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding at beginning of period, (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$25

$17.34

$17.34

'

'

'

$60.23

$60.23

$55.07

Granted (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$102.16

$58.95

$57.16

'

'

'

$102.16

$58.95

$60.23

Exercised (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$25

$17.34

$17.97

'

'

'

$58.95

$57.16

$54.51

Canceled or expired (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$36.48

$54.51

$36.48

'

'

'

$58.95

$54.51

$54.51

Outstanding at end of period, (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$36.48

$25

$17.34

'

'

'

$102.16

$60.23

$60.23

Exercisable at end of period (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$36.48

$25

$17.34

'

'

'

$60.23

$60.23

$55.07

Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding at beginning of period (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$45.20

$39.93

$36.10

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Granted (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$102.16

$58.95

$57.28

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exercised (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$41.05

$34.04

$31.37

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Canceled or expired (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$47.54

$54.51

$40.65

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Outstanding at end of period (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$68.94

$45.20

$39.93

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exercisable at end of period (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$47.72

$40.22

$37.15

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted average remaining contract life of options outstanding at end of period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'7 years 4 months 1 day

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted average remaining contract life of options exercisable at end of period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'5 years 5 months 7 days

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Aggregate intrinsic value of options outstanding at end of period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

43,289,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Aggregate intrinsic value of options exercisable at end of period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

20,004,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exercised (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-409,799

-274,842

-198,132

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Aggregate intrinsic value of options exercised

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

39,000,000

11,900,000

6,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unrecognized compensation cost expected to be recognized in future years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

38,600,000

'

'

'

2,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted-average-period expected to recognize the unrecognized compensation cost (in years)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'2 years 5 months 2 days

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted-average grant date fair value of each option granted during the period (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$34.10

$20.99

$21.57

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Dividend yield (in hundredths)

0.00%

0.00%

0.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Expected volatility (in hundredths)

37.00%

40.00%

40.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Risk-free interest rate (in hundredths)

0.90%

0.90%

2.20%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Expected life (in years)

'5 years

'5 years

'5 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Range of Exercise Price, minimum, (in dollars per share)

'

'

'

'

'

'

'

'

'

$36.48

$41.22

$42.51

$53.23

$55.84

$57.62

$58.52

$59.60

$81.20

$36.48

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Range of Exercise Price, maximum, (in dollars per share)

'

'

'

'

'

'

'

'

'

$41.21

$42.50

$53.22

$55.83

$57.61

$58.51

$59.59

$81.19

$102.16

$102.16

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, End of Period [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of Shares (in shares)

'

'

'

'

'

'

'

'

'

16,991

45,900

38,296

4,054

61,198

745

78,036

2,320

126,800

374,340

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted-Average Remaining Contractual Life (in years)

'

'

'

'

'

'

'

'

'

'4 years 11 months 7 days

'6 years 2 months 7 days

'2 years 3 months 28 days

'6 years 10 months 30 days

'7 years 2 months 0 days

'7 years 1 month 1 day

'8 years 1 month 19 days

'7 years 4 months 30 days

'9 years 2 months 7 days

'7 years 4 months 1 day

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted- Average Exercise Price (in dollars per share)

'

'

'

'

'

'

'

'

'

$37.84

$42.29

$46.14

$54.51

$57.16

$58.06

$58.95

$60.23

$102.16

$68.94

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Options Exercisable [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of Shares (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

16,991

45,900

36,037

3,243

28,930

0

13,900

1,160

0

146,161

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Weighted- Average Exercise Price (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$37.84

$42.29

$46.35

$54.51

$57.16

$0

$58.95

$60.23

$0

$47.72

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unvested restricted stock at beginning of period (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,020,673

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Granted (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

238,314

0

399,413

'

'

'

'

'

'

'

'

'

'

'

'

Vested (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-206,248

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Canceled (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-84,469

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unvested restricted stock at end of period (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

968,270

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unvested restricted stock at beginning of period (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$66.17

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Granted (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$119.84

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Vested (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$58.64

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Canceled (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$71.51

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unvested restricted stock at end of period (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$80.52

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Employee Plans [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of company match of employee contribution (in hundredths)

'

'

'

100.00%

50.00%

50.00%

'

50.00%

50.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Maximum percentage of employee total compensation matched by employer (in hundredths)

'

'

'

4.00%

6.00%

6.00%

6.00%

6.00%

6.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Company match to employee contributions (401k)

'

'

'

5,100,000

2,700,000

1,900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Administrative expense

'

'

'

0

0

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Company match to employee contributions (pension)

'

'

'

'

'

'

$280,000

$180,000

$160,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of purchase price of Company's common stock to the market price (in hundredths)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

90.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Shares available for purchase (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

34,895

46,186

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Shares of Company's common stock purchased during the period (in shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

11,291

10,153

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Schedule_II_Valuation_and_Qual2

Schedule II Valuation and Qualifying Accounts (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Valuation and Qualifying Accounts [Abstract]	'		'		'
Balance at Beginning of Year	$2,935	[1]	$2,524	[1]	$2,415	[1]
Charged to Expense	2,317	[1]	1,456	[1]	1,525	[1]
Charged to Other Accounts	0	[1],[2]	475	[1],[2]	0	[1],[2]
Write-offs, Net of Recoveries	1,855	[1]	1,520	[1]	1,416	[1]
Balance at End of Year	$3,397	[1]	$2,935	[1]	$2,524	[1]
[1]	Additions to the allowance for doubtful accounts are charged to bad debt expense.
[2]	Amounts represent opening balances from acquired businesses.