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Document And Entity Information - shares	3 Months Ended
Mar. 31, 2014	Apr. 18, 2014
Document and Entity Information [Abstract]
Entity Registrant Name	COSTAR GROUP INC
Entity Central Index Key	0001057352
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2014
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		28,768,360

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Income Statement [Abstract]
Revenues	$ 119,076	$ 104,033
Cost of revenues	33,643	33,606
Gross margin	85,433	70,427
Operating expenses:
Selling and marketing	27,745	26,978
Software development	12,351	12,102
General and administrative	24,897	29,820
Purchase amortization	3,299	4,125
Total operating expenses	68,292	73,025
Income (loss) from operations	17,141	(2,598)
Interest and other income	137	104
Interest and other expense	(1,615)	(1,755)
Income (loss) before income taxes	15,663	(4,249)
Income tax expense (benefit), net	5,923	(1,839)
Net income (loss)	$ 9,740	$ (2,410)
Net income (loss) per share-basic (in dollars per share)	$ 0.34	$ (0.09)
Net income (loss) per share-diluted (in dollars per share)	$ 0.34	$ (0.09)
Weighted average outstanding shares-basic (in shares)	28,273	27,428
Weighted average outstanding shares-diluted (in shares)	28,840	27,428

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Net income (loss)	$ 9,740	$ (2,410)
Other comprehensive income (loss), net of tax
Foreign currency translation adjustment	259	(1,640)
Net decrease in unrealized loss on investments	178	63
Total other comprehensive income (loss)	437	(1,577)
Total comprehensive income (loss)	$ 10,177	$ (3,987)

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Net Income
-URI http://asc.fasb.org/extlink&oid=6518256

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.19)
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.18)
-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.22)
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Other Comprehensive Income
-URI http://asc.fasb.org/extlink&oid=6519514

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=28358780&loc=d3e565-108580

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 19
-Article 5

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 20
-Article 9

+ Details

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 223,443	$ 255,953
Accounts receivable, less allowance for doubtful accounts of approximately $3,857 and $3,397 as of March 31, 2014 and December 31, 2013, respectively	32,286	20,761
Deferred and other income taxes, net	37,362	22,506
Prepaid expenses and other current assets	8,113	6,597
Debt issuance costs, net	2,547	2,649
Total current assets	303,751	308,466
Long-term investments	22,168	21,990
Property and equipment, net	57,338	57,719
Goodwill	718,824	718,587
Intangibles and other assets, net	137,168	144,472
Deposits and other assets	1,818	1,855
Debt issuance costs, net	3,729	3,893
Total assets	1,244,796	1,256,982
Current liabilities:
Current portion of long-term debt	26,250	24,063
Accounts payable	3,943	4,939
Accrued wages and commissions	12,426	20,104
Accrued expenses	26,208	23,200
Deferred gain on the sale of building	2,523	2,523
Income taxes payable	0	2,362
Deferred revenue	35,926	34,362
Total current liabilities	107,276	111,553
Long-term debt, less current portion	122,500	129,062
Deferred gain on the sale of building	25,655	26,286
Deferred rent	23,353	22,828
Deferred income taxes, net	31,390	34,582
Income taxes payable	4,829	4,809
Total liabilities	315,003	329,120
Stockholders' equity:
Total stockholders’ equity	929,793	927,862
Total liabilities and stockholders’ equity	$ 1,244,796	$ 1,256,982

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Operating activities:
Net income (loss)	$ 9,740	$ (2,410)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation	3,540	2,909
Amortization	6,311	7,257
Amortization of debt issuance costs	710	747
Impairment loss	1,053	0
Excess tax benefit from stock-based compensation	(23,429)	(7,305)
Stock-based compensation expense	7,879	17,326
Deferred income tax expense (benefit), net	5,090	(7,657)
Provision for losses on accounts receivable	986	321
Changes in operating assets and liabilities:
Accounts receivable	(12,499)	(8,380)
Prepaid expenses and other current assets	(1,509)	(325)
Deposits and other assets	39	322
Accounts payable and other liabilities	(5,991)	3,587
Deferred revenue	1,525	4,316
Net cash provided by (used in) operating activities	(6,555)	10,708
Investing activities:
Proceeds from sale and settlement of investments	0	83
Purchases of property and equipment and other assets	(4,149)	(4,643)
Net cash used in investing activities	(4,149)	(4,560)
Financing activities:
Payments of long-term debt	(4,375)	(4,375)
Payments of deferred consideration	(1,344)	(1,344)
Excess tax benefit from stock-based compensation	23,429	7,305
Repurchase of restricted stock to satisfy tax withholding obligations	(42,555)	(3,144)
Proceeds from exercise of stock options and employee stock purchase plan	3,001	6,807
Net cash provided by (used in) financing activities	(21,844)	5,249
Effect of foreign currency exchange rates on cash and cash equivalents	38	(30)
Net increase (decrease) in cash and cash equivalents	(32,510)	11,367
Cash and cash equivalents at the beginning of period	255,953	156,027
Cash and cash equivalents at the end of period	$ 223,443	$ 167,394

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

3 Months Ended

Mar. 31, 2014

Accounting Policies [Abstract]

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Basis of Presentation

The condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Accounting policies are consistent for each operating segment.

Interim Financial Statements

The accompanying unaudited condensed consolidated financial statements of the Company have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information. In the opinion of the Company’s management, the financial statements reflect all adjustments necessary to present fairly the Company’s financial position at March 31, 2014, the results of its operations for the three months ended March 31, 2014 and 2013, its comprehensive income for the three months ended March 31, 2014 and 2013, and its cash flows for the three months ended March 31, 2014 and 2013. These adjustments are of a normal recurring nature.

Certain notes and other information have been condensed or omitted from the interim financial statements presented in this Quarterly Report on Form 10-Q. Therefore, these financial statements should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2013.

The results of operations for the three months ended March 31, 2014 are not necessarily indicative of future financial results.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates.

Foreign Currency Translation

The Company’s functional currency in its foreign locations is the local currency. Assets and liabilities are translated into U.S. dollars as of the balance sheet dates. Revenues, expenses, gains and losses are translated at the average exchange rates in effect during each period. Gains and losses resulting from translation are included in accumulated other comprehensive income (loss). Net gains or losses resulting from foreign currency exchange transactions are included in the condensed consolidated statements of operations. There were no material gains or losses from foreign currency exchange transactions for the three months ended March 31, 2014 and 2013.


2.	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED)

Accumulated Other Comprehensive Loss

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



	March 31, 2014			December 31, 2013
Foreign currency translation adjustment	$	(3,744	)	$	(4,003	)
Accumulated net unrealized loss on investments, net of tax	(1,349		)	(1,527		)
Total accumulated other comprehensive loss	$	(5,093	)	$	(5,530	)

There were no amounts reclassified out of accumulated other comprehensive loss to the condensed consolidated statements of operations for the three months ended March 31, 2014 and 2013.

Net Income (Loss) Per Share

Net income (loss) per share is computed by dividing net income (loss) by the weighted average number of common shares outstanding during the period on a basic and diluted basis. The Company’s potentially dilutive securities include stock options and restricted stock. Diluted net income (loss) per share considers the impact of potentially dilutive securities except in periods in which there is a net loss, as the inclusion of the potentially dilutive common shares would have an anti-dilutive effect.

The following table sets forth the calculation of basic and diluted net income (loss) per share (in thousands, except per share data):



	Three Months Ended March 31,
Numerator:	2014		2013
Numerator:
Net income (loss)	$	9,740	$	(2,410	)
Denominator:
Denominator for basic net income (loss) per share — weighted-average outstanding shares	28,273		27,428
Effect of dilutive securities:
Stock options and restricted stock	567		—
Denominator for diluted net income (loss) per share — weighted-average outstanding shares	28,840		27,428

Net income (loss) per share — basic	$	0.34	$	(0.09	)
Net income (loss) per share — diluted	$	0.34	$	(0.09	)

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 (loss) per share as their inclusion would be anti-dilutive. Stock options to purchase approximately 88,000 shares that were outstanding for the three months ended March 31, 2014 were not included in the computation of diluted net income per share because the exercise price of the stock options was greater than the average market share price of the common stock during the period. The Company did not consider the impact of potentially dilutive securities for the three months ended March 31, 2013 when calculating the diluted net loss per share because the inclusion of the potentially dilutive common shares would have an anti-dilutive effect. 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.

Stock-Based Compensation

Equity instruments issued in exchange for employee services are accounted for using a fair-value based method and the fair value of such equity instruments is recognized as expense in the condensed consolidated statements of operations.


2.	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED)

Stock-Based Compensation — (Continued)

Stock-based compensation expense is measured at the grant date of the stock-based awards that vest over set time periods based on their fair values, and is recognized on a straight line basis as expense over the vesting periods of the awards, net of an estimated forfeiture rate. For equity instruments that vest based on performance, the Company assesses the probability of the achievement of the performance conditions at the end of each reporting period, or more frequently based upon the occurrence of events that may change the probability of whether the performance conditions would be met. If the Company's initial estimates of the achievement of the performance conditions change, the related stock-based compensation expense and timing of recognition may fluctuate from period to period based on those estimates. If the performance conditions are not met, no stock-based compensation expense will be recognized, and any previously recognized stock-based compensation expense will be reversed.

In 2012, the Company granted performance-based restricted common stock awards that vest upon the Company's achievement of $90.0 million of cumulative net income before interest, income taxes, depreciation and amortization ("EBITDA") over a period of four consecutive calendar quarters if such performance is achieved by March 31, 2017, subject to certain approvals under the CoStar Group, Inc. 2007 Stock Incentive Plan. As of March 31, 2014, the Company had satisfied all performance and service conditions, and as a result, the restricted common stock granted under these awards vested. The Company recorded approximately $2.2 million and $11.3 million of stock-based compensation expense related to the performance-based restricted common stock for the three months ended March 31, 2014 and 2013, respectively.

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 $3.0 million and $6.8 million for the three months ended March 31, 2014 and 2013, respectively. There were approximately $23.4 million and $7.3 million of excess tax benefits realized from stock options exercised and restricted stock awards vested for the three months ended March 31, 2014 and 2013, respectively. The effect of the excess tax benefit as of March 31, 2014 was primarily recorded in deferred and other income taxes, net and additional paid-in capital included within total stockholders' equity in the condensed consolidated balance sheets. The effect of the excess tax benefit as of December 31, 2013 was recorded in current income taxes payable and additional paid-in capital included within total stockholders' equity in the condensed consolidated balance sheets.

Stock-based compensation expense for stock options and restricted stock issued under equity incentive plans and stock purchases under the ESPP included in the Company’s results of operations were as follows (in thousands):



	Three Months Ended March 31,
	2014		2013
Cost of revenues	$	1,208	$	1,401
Selling and marketing	1,101		1,808
Software development	1,447		2,431
General and administrative	4,123		11,686
Total stock-based compensation	$	7,879	$	17,326

Options to purchase 43,416 and 146,530 shares were exercised during the three months ended March 31, 2014 and 2013, respectively.


2.	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED)

Capitalized Product Development Costs

Product development costs are expensed as incurred until technological feasibility has been established, at which time such costs are capitalized. Costs are capitalized, to the extent that the capitalizable costs do not exceed the realizable value of such costs, until the product is available for general release to customers. The Company defines the establishment of technological feasibility as the completion of all planning, designing, coding and testing activities that are necessary to establish products that meet design specifications including functions, features and technical performance requirements. The Company's capitalized product development costs had a total net book value of approximately $64,000 and $111,000 as of March 31, 2014 and December 31, 2013, respectively. These capitalized product development costs are included in intangible and other assets in the Company’s condensed consolidated balance sheets. Amortization is computed using a straight-line method over the remaining estimated economic life of the product, typically three to five years after the software is ready for its intended use. The Company amortized capitalized product development costs of approximately $47,000 for each of the three months ended March 31, 2014 and 2013.

Debt Issuance Costs

Costs incurred in connection with the issuance of long-term debt are capitalized and amortized as interest expense over the term of the related debt using the effective interest method. Upon a refinancing, previously capitalized debt issuance costs are expensed and included in loss on extinguishment of debt if the Company determines that there has been a substantial modification of the related debt. If the Company determines that there has not been a substantial modification of the related debt, any previously capitalized debt issuance costs are amortized as interest expense over the term of the new debt instrument using the effective interest method. The Company had capitalized debt issuance costs of approximately $6.3 million and $6.5 million as of March 31, 2014 and December 31, 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 “2012 Credit Agreement”). See Notes 7, 11 and 12 for additional information regarding the financing commitment with J.P. Morgan Bank and the term loan facility and revolving credit facility. The Company amortized debt issuance costs of approximately $710,000 and $747,000 for the three months ended March 31, 2014 and 2013, respectively.

Recent Accounting Pronouncements

There have been no developments to the Recent Accounting Pronouncements discussion included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2013, including the expected dates of adoption and estimated effects on the Company’s condensed consolidated financial statements.

FAIR VALUE

3 Months Ended

Mar. 31, 2014

Fair Value Disclosures [Abstract]

FAIR VALUE

Fair value is defined as the price that would be received in the sale of an asset or paid to transfer a liability in an orderly transaction between market participants. There is a three-tier fair value hierarchy, which categorizes the inputs used in measuring fair value. These tiers include: Level 1, defined as observable inputs such as quoted prices in active markets for identical assets or liabilities; Level 2, defined as inputs other than quoted prices in active markets that are either directly or indirectly observable; and Level 3, defined as unobservable inputs for which little or no market data exists, therefore requiring an entity to develop its own assumptions.

The following table represents the Company's fair value hierarchy for its financial assets (cash, cash equivalents and investments) measured at fair value on a recurring basis as of March 31, 2014 (in thousands):



	Level 1		Level 2		Level 3		Total
Assets:
Cash	$	20,358	$	—	$	—	$	20,358
Money market funds	263		—		—		263
Commercial paper	202,822		—		—		202,822
Auction rate securities	—		—		22,168		22,168
Total assets measured at fair value	$	223,443	$	—	$	22,168	$	245,611

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 Company’s Level 3 assets consist of ARS, whose underlying assets are primarily student loan securities supported by guarantees from the Federal Family Education Loan Program (“FFELP”) of the U.S. Department of Education.

The following tables summarize changes in fair value of the Company’s Level 3 assets for the three months ended March 31, 2014 and 2013 (in thousands):



	Three Months Ended March 31,
	2014		2013
Balance at beginning of period	$	21,990	$	21,662
Decrease in unrealized loss included in accumulated other comprehensive loss	178		63
Settlements	—		(50		)
Balance at end of period	$	22,168	$	21,675


4.	FAIR VALUE — (CONTINUED)

The following table summarizes changes in fair value of the Company’s Level 3 assets from December 31, 2007 to March 31, 2014 (in thousands):



	Auction Rate Securities
Balance at December 31, 2007	$	53,975
Increase in unrealized loss included in accumulated other comprehensive loss	(3,710		)
Settlements	(20,925		)
Balance at December 31, 2008	29,340
Decrease in unrealized loss included in accumulated other comprehensive loss	684
Settlements	(300		)
Balance at December 31, 2009	29,724
Decrease in unrealized loss included in accumulated other comprehensive loss	40
Settlements	(575		)
Balance at December 31, 2010	29,189
Decrease in unrealized loss included in accumulated other comprehensive loss	245
Settlements	(4,850		)
Balance at December 31, 2011	24,584
Auction rate securities upon acquisition	442
Decrease in unrealized loss included in accumulated other comprehensive loss	836
Settlements	(4,200		)
Balance at December 31, 2012	21,662
Decrease in unrealized loss included in accumulated other comprehensive loss	378
Settlements	(50		)
Balance at December 31, 2013	21,990
Decrease in unrealized loss included in accumulated other comprehensive loss	178
Settlements	—
Balance at March 31, 2014	$	22,168

ARS are variable rate debt instruments whose interest rates are reset approximately every 28 days. The majority of the underlying securities have contractual maturities greater than twenty years. The ARS are recorded at fair value.

As of March 31, 2014, the Company held ARS with $24.3 million par value, all of which failed to settle at auction. The majority of these investments are of high credit quality with AAA credit ratings and are primarily student loan securities supported by guarantees from the FFELP of the U.S. Department of Education. The Company may not be able to liquidate and fully recover the carrying value of the ARS in the near term. As a result, these securities are classified as long-term investments in the Company’s condensed consolidated balance sheet as of March 31, 2014.

While the Company continues to earn interest on its ARS investments at the contractual rate, these investments are not currently actively trading and therefore do not currently have a readily determinable market value. The estimated fair value of the ARS no longer approximates par value. The Company used a discounted cash flow model to determine the estimated fair value of its investment in ARS as of March 31, 2014. 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.


4.	FAIR VALUE — (CONTINUED)

The only significant unobservable input in the discounted cash flow model is the discount rate. The discount rate used represents the Company's estimate of the yield expected by a market participant from the ARS investments. The weighted average discount rate used in the discounted cash flow model as of March 31, 2014 and December 31, 2013 was approximately 4.9%. Selecting another discount rate within the range used in the discounted cash flow model would not result in a significant change to the fair value of the ARS.

Based on this assessment of fair value, as of March 31, 2014, the Company determined there was a decline in the fair value of its ARS investments of approximately $1.3 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 March 31, 2014, the Company had no Level 3 liabilities. As of March 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 potential deferred cash payments in connection with acquisitions LoopNet completed in 2010 including: (i) potential deferred cash payments due to the sellers of LandsofAmerica.com, LLC ("LandsofAmerica") on March 31, 2014 based on LandsofAmerica's achievement of financial and operational milestones, resulting in undiscounted deferred consideration as of December 31, 2013 of approximately $1.0 million; and (ii) potential deferred cash payments due to the sellers of Reaction Corp. ("Reaction Web") on March 31, 2014 based on Reaction Web's achievement of revenue milestones, resulting in undiscounted deferred consideration as of December 31, 2013 of approximately $344,000. On March 28, 2013, the Company paid $1.0 million to the sellers of LandsofAmerica for the achievement of financial and operational milestones in 2012 and paid approximately $344,000 to the sellers of Reaction Web for the achievement of revenue milestones in 2012. On March 31, 2014, the Company paid $1.0 million to the sellers of LandsofAmerica for the achievement of financial and operational milestones in 2013 and paid approximately $344,000 to the sellers of Reaction Web for the achievement of revenue milestones in 2013.

The following tables summarize changes in fair value of the Company’s Level 3 liabilities for the three months ended March 31, 2014 and 2013 (in thousands):



	Three Months Ended March 31,
	2014			2013
Balance at beginning of period	$	1,344		$	2,304
Accretion for period	—			126
Payments made during period	(1,344		)	(1,344		)
Balance at end of period	$	—		$	1,086

The following table summarizes changes in fair value of the Company’s Level 3 liabilities from December 31, 2012 to March 31, 2014 (in thousands):



	Deferred Consideration
Balance at December 31, 2012	$	2,304
Accretion for 2013	384
Payments made in 2013	(1,344		)
Balance at December 31, 2013	1,344
Payments made from January 1, 2014 – March 31, 2014	(1,344		)
Balance at March 31, 2014	$	—


4.	FAIR VALUE — (CONTINUED)

Prior to December 31, 2013, 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 included 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 was the discount rate. The discount rate used represented LoopNet's cost of equity at the time of each acquisition plus a margin for counterparty risk. As of December 31, 2013, the Company recorded a liability for the entire amount of undiscounted deferred consideration paid on March 31, 2014.

Concentration of Credit Risk and Financial Instruments

The Company performs ongoing credit evaluations of its customers’ financial condition and generally does not require that its customers’ obligations to the Company be secured. The Company maintains reserves for estimated inherent credit losses, and such losses have been within management’s expectations. The large size and widespread nature of the Company’s customer base and the Company’s lack of dependence on any individual customer mitigates the risk of nonpayment of the Company’s accounts receivable. The carrying amount of the accounts receivable approximates the net realizable value. The carrying value of accounts receivable, accounts payable, accrued expenses, and long-term debt approximates fair value.

- Definition

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

+ References + Details

LONG-TERM DEBT	3 Months Ended
LONG-TERM DEBT	Mar. 31, 2014
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 2012 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 2012 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 2012 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 2012 Credit Agreement, the interest rate on overdue amounts will increase by 2.00% per annum. The obligations under the 2012 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 2012 Credit Agreement requires the Company to maintain a Debt Service Coverage Ratio (as defined in the 2012 Credit Agreement) of at least 1.5 to 1.0 and a Total Leverage Ratio (as defined in the 2012 Credit Agreement) that does not exceed 2.75 to 1.00 during each of the three months ending March 31, 2014 and June 30, 2014; and 2.50 to 1.00 thereafter. The 2012 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 to (i) incur additional indebtedness, (ii) create, incur, assume or permit to exist any liens, (iii) enter into mergers, consolidations or similar transactions, (iv) make investments and acquisitions, (v) make certain dispositions of assets, (vi) make dividends, distributions and prepayments of certain indebtedness, and (vii) enter into certain transactions with affiliates. The Company was in compliance with the covenants in the 2012 Credit Agreement as of March 31, 2014. Commencing with the fiscal year ended December 31, 2012, the 2012 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 2012 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 2012 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 2012 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 2012 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 March 31, 2014 and December 31, 2013, no amounts were outstanding under the revolving credit facility. Total interest expense for the term loan facility was approximately $1.6 million and $1.8 million for the three months ended March 31, 2014 and 2013, respectively. Interest expense included amortized debt issuance costs of approximately $710,000 and $747,000 for the three months ended March 31, 2014 and 2013, respectively. Total interest paid for the term loan facility was approximately $905,000 and $1.4 million for the three months ended March 31, 2014 and 2013, respectively. See Note 11 for details on the February 2014 financing commitment letter from JPMorgan Chase Bank, N.A., Bank of America, N.A., SunTrust Bank and Wells Fargo Bank, National Association and see Note 12 for details on the related term loan facility and revolving credit facility provided to the Company in April 2014.

COMMITMENTS AND CONTINGENCIES

3 Months Ended

Mar. 31, 2014

Commitments and Contingencies Disclosure [Abstract]

COMMITMENTS AND CONTINGENCIES

The Company leases office facilities and office equipment under various non-cancelable operating leases. The leases contain various renewal options.

On February 16, 2012, the Company entered into the 2012 Credit Agreement. The 2012 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 7 for additional information regarding the 2012 Credit Agreement. See Note 11 for details on the February 2014 financing commitment letter from JPMorgan Chase Bank, N.A., Bank of America, N.A., SunTrust Bank and Wells Fargo Bank, National Association and see Note 12 for details on the repayment and termination of the 2012 Credit Agreement and the term loan facility and revolving credit facility provided to the Company in April 2014.

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, the plaintiffs filed a third supplemental submission in support of their motion for preliminary approval of the proposed settlement. The show cause hearing is scheduled for May 13, 2014.


9.	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 violated 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. On April 9, 2014 the Company offered to settle all outstanding litigation with Civix for $1.2 million. 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 $2.5 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 condensed consolidated financial statements for unfavorable results, if any, other than described above. Legal defense costs are expensed as incurred.

SEGMENT REPORTING

3 Months Ended

Mar. 31, 2014

Segment Reporting [Abstract]

SEGMENT REPORTING

The Company manages its business geographically in two operating segments, with the primary areas of measurement and decision-making being the U.S. and International, which includes the U.K. and France. The Company’s subscription-based information services consist primarily of CoStar Suite^TM and FOCUS^TM 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 (loss) before interest, income taxes, depreciation and amortization. Management believes that operating segment EBITDA is an appropriate measure for evaluating the operational performance of the Company's operating segments. EBITDA is used by management to internally measure operating and management performance and to evaluate the performance of the business. However, this measure should be considered in addition to, not as a substitute for or superior to, income from operations or other measures of financial performance prepared in accordance with GAAP.

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



	Three Months Ended March 31,
	2014		2013
Revenues
United States	$	113,326	$	99,296
International
External customers	5,750		4,737
Intersegment revenue	—		116
Total international revenue	5,750		4,853
Intersegment eliminations	—		(116		)
Total revenues	$	119,076	$	104,033

EBITDA
United States	$	26,368	$	9,286
International	624		(1,718		)
Total EBITDA	$	26,992	$	7,568



Reconciliation of EBITDA to net income (loss)
EBITDA	$	26,992		$	7,568
Purchase amortization in cost of revenues	(2,877		)	(3,027		)
Purchase amortization in operating expenses	(3,299		)	(4,125		)
Depreciation and other amortization	(3,675		)	(3,014		)
Interest income	137			104
Interest expense	(1,615		)	(1,755		)
Income tax expense, net	(5,923		)	1,839
Net income (loss)	$	9,740		$	(2,410	)

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.


10.	SEGMENT REPORTING — (CONTINUED)

U.S. EBITDA includes an allocation of approximately $400,000 for the three months ended March 31, 2014. This allocation represents costs incurred for International employees involved in development activities of the Company's U.S. operating segment. There were no costs allocated to U.S. EBITDA for the three months ended March 31, 2013.

International EBITDA includes a corporate allocation of approximately $100,000 for each of the three months ended March 31, 2014 and 2013. 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):



	March 31, 2014			December 31, 2013
Property and equipment, net
United States	$	53,670		$	53,733
International	3,668			3,986
Total property and equipment, net	$	57,338		$	57,719

Goodwill
United States	$	692,639		$	692,639
International	26,185			25,948
Total goodwill	$	718,824		$	718,587

Assets
United States	$	1,298,378		$	1,311,292
International	44,163			43,464
Total operating segment assets	$	1,342,541		$	1,354,756

Reconciliation of operating segment assets to total assets
Total operating segment assets	$	1,342,541		$	1,354,756
Investment in subsidiaries	(18,344		)	(18,344		)
Intersegment receivables	(79,401		)	(79,430		)
Total assets	$	1,244,796		$	1,256,982

Liabilities
United States	$	310,048		$	324,626
International	80,289			79,266
Total operating segment liabilities	$	390,337		$	403,892

Reconciliation of operating segment liabilities to total liabilities
Total operating segment liabilities	$	390,337		$	403,892
Intersegment payables	(75,334		)	(74,772		)
Total liabilities	$	315,003		$	329,120

- Definition

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

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+ Details

PENDING ACQUISITION	3 Months Ended
PENDING ACQUISITION	Mar. 31, 2014
Business Combinations [Abstract]
Pending Acquisition [Text Block]	PENDING ACQUISITION On February 28, 2014, the Company and Classified Ventures, LLC (“CV”) entered into an Asset Purchase Agreement (the “Asset Purchase Agreement”). Pursuant to the Asset Purchase Agreement, the Company agreed to purchase from CV certain assets and assume certain liabilities, in each case, related to the Apartments.com business for $585.0 million in cash, subject to a customary working capital adjustment. The boards of directors of both companies unanimously approved the transaction. The completion of the acquisition is subject to customary conditions, including, among others, the expiration or termination of any applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended. The transaction is not subject to a financing condition. The Asset Purchase Agreement may be terminated by both the Company and CV under certain circumstances, including if the acquisition is not consummated by August 28, 2014. The Asset Purchase Agreement contains certain termination rights for both the Company and CV, and further provides that, upon the termination of the Asset Purchase Agreement under specified circumstances in which certain antitrust approvals are not obtained or a governmental order related to antitrust or competition matters prohibits the consummation of the acquisition, the Company will be required to pay to CV a cash termination fee of $17.6 million. In connection with the acquisition, JPMorgan Chase Bank, N.A., Bank of America, N.A., SunTrust Bank and Wells Fargo Bank, National Association committed to provide the Company with a $400.0 million senior secured term loan facility (the “Initial Term Facility”) and a $225.0 million senior secured revolving credit facility (the “Revolving Facility” and, collectively with the Initial Term Facility, the “Credit Facilities”), on the terms and subject to the conditions set forth in a debt commitment letter dated February 28, 2014. The proceeds of the Credit Facilities, together with cash on hand, will be used to finance the consideration due to CV under the Asset Purchase Agreement, to pay all principal, accrued and unpaid interest, fees, premiums, if any, and other amounts due under the 2012 Credit Agreement, to fund any original issue discount or upfront fees to the extent permitted and, in the case of the Revolving Facility, for working capital and other general corporate purposes. The Initial Term Facility will mature on the date that is five years after the completion of the acquisition and will amortize in quarterly installments equal to 5% of the original principal amount of the Initial Term Facility during each of the first, second and third years, 10% during the fourth year, and 15% during the fifth year, with the remainder payable at final maturity. The Revolving Facility will mature and terminate five years after the completion of the acquisition. The Company’s obligations under the Credit Facilities will be guaranteed (subject to certain exceptions) on a senior basis by each existing and subsequently acquired or organized direct or indirect wholly-owned restricted subsidiary of the Company (the “Subsidiary Guarantors”) and will be secured (subject to permitted liens and other agreed upon exceptions) on a first priority basis by a security interest in substantially all of the assets of CoStar and the Subsidiary Guarantors and a pledge of 100% (subject to certain exceptions) of the equity interests in each direct restricted subsidiary of Costar and each Subsidiary Guarantor. As a result of the pending acquisition of the Apartments.com business, the Company recorded approximately $1.1 million in acquisition-related costs for the three months ended March 31, 2014. The Company is not in a position yet to estimate with certainty the financial impact the proposed acquisition will have on its operations. See Note 12 for further details regarding the closing of the acquisition of the Apartments.com business on April 1, 2014 as well as the repayment and termination of the 2012 Credit Agreement and the term loan facility and revolving credit facility provided to the Company on April 1, 2014.

- Definition

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

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-SubTopic 30
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=7488404&loc=d3e7000-128479

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6910749&loc=d3e4922-128472

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6910749&loc=d3e4934-128472

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6910749&loc=d3e4926-128472

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1383-128463

Reference 15: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=7488404&loc=d3e6996-128479

+ Details

SUBSEQUENT EVENTS

3 Months Ended

Mar. 31, 2014

Subsequent Events [Abstract]

Subsequent Events [Text Block]

SUBSEQUENT EVENTS

As discussed in Note 11, on February 28, 2014, the Company and CV entered into the Asset Purchase Agreement. Pursuant to the Asset Purchase Agreement, on April 1, 2014 (the “Closing Date”), the Company purchased from CV certain assets and assumed certain liabilities, in each case, related to the Apartments.com business (collectively, the “Business”) for $585.0 million in cash, subject to a customary working capital adjustment. The purchase price paid at closing was $587.1 million, which reflected an estimated $2.1 million increase in net working capital of the Business as of the closing date over the threshold net working capital amount; this amount is subject to further adjustment once the final net working capital of the Business as of the closing date is determined. The Company is not in a position yet to estimate with certainty the financial impact the acquisition will have on its operations.


12.	SUBSEQUENT EVENTS — (CONTINUED)

On the Closing Date, the Company entered into a Credit Agreement (the “2014 Credit Agreement”) by and among CoStar, as Borrower, CoStar Realty Information, Inc., as Co-Borrower, the Lenders from time to time party thereto and JPMorgan Chase Bank, N.A., as Administrative Agent. The 2014 Credit Agreement provides for a $400.0 million term loan facility and a $225.0 million revolving credit facility, each with a term of five years. The proceeds of the term loan facility and the initial borrowing under the revolving credit facility on the Closing Date in an amount of $150.0 million were used to refinance the 2012 Credit Agreement, including related fees and expenses, and pay a portion of the consideration and transaction costs related to the acquisition. The undrawn proceeds of the revolving credit facility will be available for working capital and other general corporate purposes of CoStar and its subsidiaries.

Effective April 1, 2014, the Company terminated the 2012 Credit Agreement and repaid all amounts outstanding thereunder. The Company evaluated the debt modification and determined that the modification did not qualify as an extinguishment of debt because the change in the present value of future cash flows between the initial term loan facility and the new term loan facility was not considered a substantial modification.

The revolving credit facility includes a subfacility for swingline loans of up to $10.0 million, and up to $10.0 million of the revolving credit facility is available for the issuance of letters of credit. The term loan facility will amortize in quarterly installments in amounts resulting in an annual amortization of 5% during each of the first, second and third years, 10% during the fourth year and 15% during the fifth year after the Closing Date, with the remainder payable at final maturity. The loans under the 2014 Credit Agreement bear interest, at the option of CoStar, either (i) during any interest period selected by CoStar, at the London interbank offered rate for deposits in U.S. dollars with a maturity comparable to such interest period, adjusted for statutory reserves (“LIBOR”), plus an initial spread of 2.00% per annum, subject to adjustment based on the First Lien Secured Leverage Ratio (as defined in the 2014 Credit Agreement) of the Company, or (ii) at the greatest of (x) the prime rate from time to time announced by JPMorgan Chase Bank, N.A., (y) the federal funds effective rate plus ½ of 1% and (z) LIBOR for a one-month interest period plus 1.00%, plus an initial spread of 1.00% per annum, subject to adjustment based on the First Lien Secured Leverage Ratio of the Company. If an event of default occurs under the 2014 Credit Agreement, the interest rate on overdue amounts will increase by 2.00% per annum. The obligations under the 2014 Credit Agreement are guaranteed by all material subsidiaries of CoStar and are secured by a lien on substantially all of the assets of CoStar and its material subsidiaries, in each case subject to certain exceptions, pursuant to security and guarantee documents entered into on the Closing Date.

The 2014 Credit Agreement requires the Company to maintain (i) a First Lien Secured Leverage Ratio not exceeding 4.00 to 1.00 during the first eight full fiscal quarters after the Closing Date, and 3.50 to 1.00 thereafter and (ii) after the incurrence of additional indebtedness under certain specified exceptions in the 2014 Credit Agreement, a Total Leverage Ratio (as defined in the 2014 Credit Agreement) not exceeding 5.00 to 1.00 during the first eight full fiscal quarters after the Closing Date, and 4.50 to 1.00 thereafter. The 2014 Credit Agreement also includes other covenants, including covenants that, subject to certain exceptions, restrict the ability of the Company and its subsidiaries to (i) incur additional indebtedness, (ii) create, incur, assume or permit to exist any liens, (iii) enter into mergers, consolidations or similar transactions, (iv) make investments and acquisitions, (v) make certain dispositions of assets, (vi) make dividends, distributions and prepayments of certain indebtedness, and (vii) enter into certain transactions with affiliates.

In connection with obtaining the term loan facility and revolving credit facility pursuant to the 2014 Credit Agreement, the Company incurred approximately $10.4 million in debt issuance costs as of April 1, 2014. The debt issuance costs were comprised of approximately $9.7 million in underwriting fees and approximately $700,000 primarily related to legal fees associated with the debt issuance. Approximately $10.2 million of the fees associated with the refinancing, along with the unamortized debt issuance cost from the 2012 Credit Agreement are capitalized and amortized as interest expense over the term of the 2014 Credit Agreement using the effective interest method.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

3 Months Ended

Mar. 31, 2014

Accounting Policies [Abstract]

Basis of Presentation

Use of Estimates

Foreign Currency Translation

Accumulated Other Comprehensive Loss

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



	March 31, 2014			December 31, 2013
Foreign currency translation adjustment	$	(3,744	)	$	(4,003	)
Accumulated net unrealized loss on investments, net of tax	(1,349		)	(1,527		)
Total accumulated other comprehensive loss	$	(5,093	)	$	(5,530	)

There were no amounts reclassified out of accumulated other comprehensive loss to the condensed consolidated statements of operations for the three months ended March 31, 2014 and 2013.

Net Income Per Share

Net Income (Loss) Per Share

Stock-Based Compensation


2.	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES — (CONTINUED)

Stock-Based Compensation — (Continued)

Capitalized Product Development Costs

Debt Issuance Costs

Recent Accounting Pronouncements

FAIR VALUE (Tables)

3 Months Ended

Mar. 31, 2014

Fair Value Disclosures [Abstract]

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



	Level 1		Level 2		Level 3		Total
Assets:
Cash	$	20,358	$	—	$	—	$	20,358
Money market funds	263		—		—		263
Commercial paper	202,822		—		—		202,822
Auction rate securities	—		—		22,168		22,168
Total assets measured at fair value	$	223,443	$	—	$	22,168	$	245,611



	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

Summary of changes in the fair value of the company's level 3 assets

The following tables summarize changes in fair value of the Company’s Level 3 assets for the three months ended March 31, 2014 and 2013 (in thousands):



	Three Months Ended March 31,
	2014		2013
Balance at beginning of period	$	21,990	$	21,662
Decrease in unrealized loss included in accumulated other comprehensive loss	178		63
Settlements	—		(50		)
Balance at end of period	$	22,168	$	21,675


4.	FAIR VALUE — (CONTINUED)

The following table summarizes changes in fair value of the Company’s Level 3 assets from December 31, 2007 to March 31, 2014 (in thousands):



	Auction Rate Securities
Balance at December 31, 2007	$	53,975
Increase in unrealized loss included in accumulated other comprehensive loss	(3,710		)
Settlements	(20,925		)
Balance at December 31, 2008	29,340
Decrease in unrealized loss included in accumulated other comprehensive loss	684
Settlements	(300		)
Balance at December 31, 2009	29,724
Decrease in unrealized loss included in accumulated other comprehensive loss	40
Settlements	(575		)
Balance at December 31, 2010	29,189
Decrease in unrealized loss included in accumulated other comprehensive loss	245
Settlements	(4,850		)
Balance at December 31, 2011	24,584
Auction rate securities upon acquisition	442
Decrease in unrealized loss included in accumulated other comprehensive loss	836
Settlements	(4,200		)
Balance at December 31, 2012	21,662
Decrease in unrealized loss included in accumulated other comprehensive loss	378
Settlements	(50		)
Balance at December 31, 2013	21,990
Decrease in unrealized loss included in accumulated other comprehensive loss	178
Settlements	—
Balance at March 31, 2014	$	22,168

Summary of changes in the fair value of the company's level 3 liabilities

The following tables summarize changes in fair value of the Company’s Level 3 liabilities for the three months ended March 31, 2014 and 2013 (in thousands):



	Three Months Ended March 31,
	2014			2013
Balance at beginning of period	$	1,344		$	2,304
Accretion for period	—			126
Payments made during period	(1,344		)	(1,344		)
Balance at end of period	$	—		$	1,086

The following table summarizes changes in fair value of the Company’s Level 3 liabilities from December 31, 2012 to March 31, 2014 (in thousands):



	Deferred Consideration
Balance at December 31, 2012	$	2,304
Accretion for 2013	384
Payments made in 2013	(1,344		)
Balance at December 31, 2013	1,344
Payments made from January 1, 2014 – March 31, 2014	(1,344		)
Balance at March 31, 2014	$	—

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, NET INCOME (LOSS) PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Numerator: [Abstract]
Net income (loss)	$ 9,740	$ (2,410)
Denominator: [Abstract]
Denominator for basic net income (loss) per share - weighted-average outstanding shares (in shares)	28,273	27,428
Effect of dilutive securities: [Abstract]
Stock options and restricted stock	567	0
Denominator for diluted net income (loss) per share - weighted-average outstanding shares (in shares)	28,840	27,428
Net income (loss) per share - basic (in dollars per share)	$ 0.34	$ (0.09)
Net income (loss) per share - diluted (in dollars per share)	$ 0.34	$ (0.09)
Antidilutive securities excluded from computation of earnings per share	88	0

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, ACCUMULATED OTHER COMPREHENSIVE LOSS, NET OF TAX (Details) - USD ($)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Accounting Policies [Abstract]
Material gains or losses from foreign currency transactions	$ 0	$ 0
Accumulated Other Comprehensive Loss Net of Tax [Abstract]
Foreign currency translation adjustment	(3,744,000)		$ (4,003,000)
Accumulated net unrealzied loss on investments, net of tax	(1,349,000)		(1,527,000)
Total accumulated other comprehensive loss	(5,093,000)		$ (5,530,000)
Reclassification out of accumulated other comprehensive loss	$ 0	$ 0

- Definition

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

+ References + Details

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, STOCK BASED COMPENSATION EXPENSE (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2014 USD ($) quarters shares	Mar. 31, 2013 USD ($) shares
Stock-Based Compensation Expense [Abstract]
Compensation expense	$ 7,879	$ 17,326
Net cash proceeds from the exercise of stock options and ESPP	3,001	6,807
Excess tax benefits realized from stock option exercised and restricted stock awards vested	$ 23,429	$ 7,305
Exercise of stock options (in shares) \| shares	43,416	146,530
Cost of Revenues [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	$ 1,208	$ 1,401
Selling and Marketing [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	1,101	1,808
Software Development [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	1,447	2,431
General and Administrative [Member]
Stock-Based Compensation Expense [Abstract]
Compensation expense	4,123	11,686
Performance-Based Restricted Common Stock [Member]
Stock-Based Compensation Expense [Abstract]
Cumulative EBITDA required for award shares to vest	$ 90,000
Number of consecutive quarters to mantain cumulative EBITDA required for award shares to vest \| quarters	4
Compensation expense	$ 2,200	$ 11,300

INVESTMENTS (Details) - USD ($)	3 Months Ended
INVESTMENTS (Details) - USD ($)	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, gross realized gains	$ 0	$ 0
Available-for-sale securities, gross realized losses	0	$ 0
Debt Maturities Fair Value [Abstract]
April 1, 2014 — March 31, 2015	0
April 1, 2015 — March 31, 2019	851,000
April 1, 2019 — March 31, 2024	0
After March 31, 2024	21,317,000
Fair Value	$ 22,168,000		$ 21,990,000

INVESTMENTS, AVAILABLE-FOR-SALE SECURITIES (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	$ 0	$ 0
Available-for-sale Securities Reconciliation [Abstract]
Amortized Cost	23,517	23,517
Gross Unrealized Gains	409	411
Gross Unrealized Losses	(1,758)	(1,938)
Fair Value	22,168	21,990
Available-for-sale securities, unrealized loss positions
Aggregate Fair Value	21,317	21,137
Auction Rate Securities [Member]
Available-for-sale Securities Reconciliation [Abstract]
Amortized Cost	23,517	23,517
Gross Unrealized Gains	409	411
Gross Unrealized Losses	(1,758)	(1,938)
Fair Value	22,168	21,990
Available-for-sale securities, unrealized loss positions
Aggregate Fair Value	$ 21,317	$ 21,137

FAIR VALUE (Details) - USD ($)	3 Months Ended		12 Months Ended
FAIR VALUE (Details) - USD ($)	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Mar. 28, 2013
Unobservable inputs assets (level 3) [Roll forward]
Beginning balance	$ 21,990,000	$ 21,662,000	$ 21,662,000
Change in unrealized gain (loss) included in accumulated other comprehensive loss	178,000	63,000
Settlements	0	(50,000)
Ending balance	$ 22,168,000	21,675,000	$ 21,990,000	$ 21,662,000
Auction rate securities variable rate debt instruments interest rate reset period	28 days
The minimum contractual maturities on underlying securities involved in auction rate securities	20 years
Par value of company held auction rate securities	$ 24,300,000
Discount rate (in percent)	4.90%		4.90%
Temporary impairment of the auction rates security investments	$ (1,349,000)		$ (1,527,000)
Unobservable inputs liabilities (level 3) [Roll forward]
Beginning balance	1,344,000	2,304,000	2,304,000
Accretion	0	126,000	384,000
Payments	(1,344,000)	(1,344,000)	(1,344,000)
Ending balance	0	1,086,000	1,344,000	2,304,000
Fair Value, Measurements, Recurring [Member]
Assets:
Total assets measured at fair value	245,611,000		277,943,000
Liabilities:
Deferred consideration			1,344,000
Fair Value, Measurements, Recurring [Member] \| Cash [Member]
Assets:
Total assets measured at fair value	20,358,000		134,989,000
Fair Value, Measurements, Recurring [Member] \| Money Market Funds [Member]
Assets:
Total assets measured at fair value	263,000		50,593,000
Fair Value, Measurements, Recurring [Member] \| Commercial Paper [Member]
Assets:
Total assets measured at fair value	202,822,000		70,371,000
Fair Value, Measurements, Recurring [Member] \| Auction Rate Securities [Member]
Assets:
Total assets measured at fair value	22,168,000		21,990,000
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member]
Assets:
Total assets measured at fair value	223,443,000		255,953,000
Liabilities:
Deferred consideration			0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Cash [Member]
Assets:
Total assets measured at fair value	20,358,000		134,989,000
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Money Market Funds [Member]
Assets:
Total assets measured at fair value	263,000		50,593,000
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Commercial Paper [Member]
Assets:
Total assets measured at fair value	202,822,000		70,371,000
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 1 [Member] \| Auction Rate Securities [Member]
Assets:
Total assets measured at fair value	0		0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Assets:
Total assets measured at fair value	0		0
Liabilities:
Deferred consideration			0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Cash [Member]
Assets:
Total assets measured at fair value	0		0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Money Market Funds [Member]
Assets:
Total assets measured at fair value	0		0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Commercial Paper [Member]
Assets:
Total assets measured at fair value	0		0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member] \| Auction Rate Securities [Member]
Assets:
Total assets measured at fair value	0		0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member]
Assets:
Total assets measured at fair value	22,168,000		21,990,000
Liabilities:
Deferred consideration	0		1,344,000
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Cash [Member]
Assets:
Total assets measured at fair value	0		0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Money Market Funds [Member]
Assets:
Total assets measured at fair value	0		0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Commercial Paper [Member]
Assets:
Total assets measured at fair value	0		0
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 3 [Member] \| Auction Rate Securities [Member]
Assets:
Total assets measured at fair value	22,168,000		21,990,000
Auction Rate Securities [Member]
Unobservable inputs assets (level 3) [Roll forward]
Beginning balance	21,990,000	$ 21,662,000	21,662,000	24,584,000	$ 29,189,000	$ 29,724,000	$ 29,340,000	$ 53,975,000
Change in unrealized gain (loss) included in accumulated other comprehensive loss	178,000		378,000	836,000	245,000	40,000	684,000	(3,710,000)
Settlements	0		(50,000)	(4,200,000)	(4,850,000)	(575,000)	(300,000)	(20,925,000)
Auction rate securities upon acquisition				442,000
Ending balance	22,168,000		21,990,000	$ 21,662,000	$ 24,584,000	$ 29,189,000	$ 29,724,000	$ 29,340,000
LandsofAmerica [Member]
Unobservable inputs liabilities (level 3) [Roll forward]
Business acquisition deferred consideration potential cash payment (undiscounted)			1,000,000
Business acquisition deferred consideration cash payment	1,000,000								$ 1,000,000
Reaction Web [Member]
Unobservable inputs liabilities (level 3) [Roll forward]
Business acquisition deferred consideration potential cash payment (undiscounted)			$ 344,000
Business acquisition deferred consideration cash payment	$ 344,000								$ 344,000

INTANGIBLES AND OTHER ASSETS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Apr. 30, 2012
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, net	$ 137,168		$ 144,472
Impairment of intangible assets, finite-lived	1,053	$ 0
Capitalized Product Development Costs [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	2,140		2,140
Finite-lived intangible assets, accumulated amortization	(2,076)		(2,029)
Finite-lived intangible assets, net	$ 64		111
Weighted-average amortization period (in years}	4 years
Building Photography [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 13,804		13,743
Finite-lived intangible assets, accumulated amortization	(12,154)		(12,005)
Finite-lived intangible assets, net	$ 1,650		1,738
Weighted-average amortization period (in years}	5 years
Acquired Database Technology [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 77,386		77,368
Finite-lived intangible assets, accumulated amortization	(43,823)		(41,073)
Finite-lived intangible assets, net	$ 33,563		36,295
Weighted-average amortization period (in years}	5 years
Acquired Customer Base [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 131,089		130,960
Finite-lived intangible assets, accumulated amortization	(78,167)		(74,734)
Finite-lived intangible assets, net	$ 52,922		56,226
Weighted-average amortization period (in years}	10 years
Acquired Trade Names and Other [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross	$ 57,552		59,336
Finite-lived intangible assets, accumulated amortization	(8,583)		(9,234)
Finite-lived intangible assets, net	$ 48,969		$ 50,102
Weighted-average amortization period (in years}	7 years
LoopNet [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Business acquisition, purchase price allocation, intangible assets not amortizable				$ 48,700

LONG-TERM DEBT LONG-TERM DEBT (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Feb. 16, 2012	Mar. 31, 2014	Mar. 31, 2013	Jun. 30, 2012	Apr. 01, 2014	Dec. 31, 2013	Apr. 30, 2012
Business Acquisition [Line Items]
Line of credit facility, amount outstanding					$ 150,000	$ 0
LIBOR maturity period (in months)	1 month
Default interest rate per annum on overdue amounts (in percent)	2.00%
Maximum debt service coverage ratio for two quarters after closing (in percent)	150.00%
Maximum total leverage ratio for fifth through eighth quarters after closing date (in percent)	275.00%
Maximum total leverage ratio after eight fiscal quarters (in percent)	250.00%
First Excess Cash Flow Repayment, Percentage (in percent)	50.00%
Second Excess Cash Flow Repayment, Percentage (in percent)	25.00%
Third Excess Cash Flow Repayment, Percentage (in percent)	0.00%
Excess Cash Flow Payment Maturity Period Within Issuance of Financial Statements	10 days
Unamortized Debt Issuance Expense				$ 11,500
Debt issuance underwriting fees				9,200
Legal fees associated with the debt issuance				$ 2,300
Amortization of debt issuance costs		$ 710	$ 747
Interest paid		905	1,371
Revolving Credit Facility [Member]
Business Acquisition [Line Items]
Line of credit facility, amount outstanding		0
New Term Loan [Member]
Business Acquisition [Line Items]
Interest expense, debt		$ 1,615	$ 1,755
LoopNet [Member]
Business Acquisition [Line Items]
Credit facility, collateral	The obligations under the 2012 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.
CoStar Group [Member] \| LoopNet [Member] \| Committed Term Loan [Member]
Business Acquisition [Line Items]
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%
CoStar Group [Member] \| LoopNet [Member] \| Revolving Credit Facility [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity	$ 50,000
Term of loan (in years)	5 years
CoStar Group [Member] \| LoopNet [Member] \| New Term Loan [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity	$ 175,000
Term of loan (in years)	5 years
Line of credit facility, amount outstanding							$ 175,000
Minimum [Member]
Business Acquisition [Line Items]
First Excess Cash Flow Repayment Requirement (in percent)	300.00%
Second Excess Cash Flow Repayment Requirement (in percent)	250.00%
Maximum [Member]
Business Acquisition [Line Items]
Second Excess Cash Flow Repayment Requirement (in percent)	300.00%
Third Excess Cash Flow Repayment Requirement (in percent	250.00%
Maximum [Member] \| CoStar Group [Member] \| Swingline Loan [Member]
Business Acquisition [Line Items]
Revolving credit sub-facility for swing-line loans and issuances of letters of credit	$ 5,000
Maximum [Member] \| CoStar Group [Member] \| Letter of Credit [Member]
Business Acquisition [Line Items]
Revolving credit sub-facility for swing-line loans and issuances of letters of credit	$ 10,000
LIBOR [Member]
Business Acquisition [Line Items]
Basis spread on federal funds rate (in percent)	2.00%
Debt instrument, basis spread on variable rate, one month interest period (in percent)	1.00%
Debt instrument, basis spread on variable rate, per annum (in percent)	1.00%
Federal Funds Rate [Member]
Business Acquisition [Line Items]
Basis spread on federal funds rate (in percent)	0.50%

COMMITMENTS AND CONTINGENCIES (Details)			1 Months Ended
COMMITMENTS AND CONTINGENCIES (Details)	Nov. 25, 2013 USD ($)	Feb. 16, 2012 USD ($)	May 31, 2011 class_action_lawsuits	Mar. 31, 2014 USD ($) current_litigation_matters	Nov. 05, 2013 USD ($)
Business Acquisition [Line Items]
Class action lawsuits brought by alleged LoopNet stockholders (in lawsuits) \| class_action_lawsuits			3
Loss contingency, value of damages sought	$ 3,700,000
Minimum number of current litigation matters \| current_litigation_matters				1
New Term Loan [Member] \| CoStar Group [Member] \| LoopNet [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity		$ 175,000,000
Term of loan (in years)		5 years
Revolving Credit Facility [Member] \| CoStar Group [Member] \| LoopNet [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity		$ 50,000,000
Term of loan (in years)		5 years
Civix [Member]
Business Acquisition [Line Items]
Loss contingency accrual				$ 1,200,000	$ 600,000
Loss contingency in excess of amount accrued				2,500,000
LoopNet Stockholders [Member]
Business Acquisition [Line Items]
Loss contingency accrual				$ 200,000

SEGMENT REPORTING (Details)	3 Months Ended
SEGMENT REPORTING (Details)	Mar. 31, 2014 USD ($) operating_segments	Mar. 31, 2013 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Segment Reporting Information [Line Items]
Number of business segments (in segments) \| operating_segments	2
Summarized information by operating segment [Abstract]
Revenues	$ 119,076,000	$ 104,033,000
Property and equipment, net	57,338,000		$ 57,719,000
Goodwill	718,824,000		718,587,000	$ 718,078,000
Reconciliation of EBITDA to net income (loss) [Abstract]
EBITDA	26,992,000	7,568,000
Purchase amortization in cost of revenues	(2,877,000)	(3,027,000)
Purchase amortization in operating expenses	(3,299,000)	(4,125,000)
Depreciation and other amortization	(3,675,000)	(3,014,000)
Interest income	137,000	104,000
Interest expense	(1,615,000)	(1,755,000)
Income tax expense, net	(5,923,000)	1,839,000
Net income (loss)	9,740,000	(2,410,000)
Reconciliation of operating segment assets to total assets [Abstract]
Total operating segment assets	1,342,541,000		1,354,756,000
Investment in subsidiaries	(18,344,000)		(18,344,000)
Intersegment receivables	(79,401,000)		(79,430,000)
Total assets	1,244,796,000		1,256,982,000
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total operating segment liabilities	390,337,000		403,892,000
Intersegment payables	(75,334,000)		(74,772,000)
Total liabilities	315,003,000		329,120,000
United States [Member]
Segment Reporting Information [Line Items]
U.S. corporate allocation	400,000	0
Summarized information by operating segment [Abstract]
Revenues	113,326,000	99,296,000
Property and equipment, net	53,670,000		53,733,000
Goodwill	692,639,000		692,639,000	692,639,000
Reconciliation of EBITDA to net income (loss) [Abstract]
EBITDA	26,368,000	9,286,000
Reconciliation of operating segment assets to total assets [Abstract]
Total operating segment assets	1,298,378,000		1,311,292,000
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total operating segment liabilities	310,048,000		324,626,000
International [Member]
Segment Reporting Information [Line Items]
International corporate allocation	100,000	100,000
Summarized information by operating segment [Abstract]
Revenues	5,750,000	4,853,000
Property and equipment, net	3,668,000		3,986,000
Goodwill	26,185,000		25,948,000	$ 25,439,000
Reconciliation of EBITDA to net income (loss) [Abstract]
EBITDA	624,000	(1,718,000)
Reconciliation of operating segment assets to total assets [Abstract]
Total operating segment assets	44,163,000		43,464,000
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total operating segment liabilities	80,289,000		$ 79,266,000
External Customers [Member]
Summarized information by operating segment [Abstract]
Revenues	5,750,000	4,737,000
Intersegment Revenue [Member]
Summarized information by operating segment [Abstract]
Revenues	0	116,000
Intersegment Elimination [Member]
Summarized information by operating segment [Abstract]
Revenues	$ 0	$ (116,000)

PENDING ACQUISITION (Details) - USD ($) $ in Thousands		3 Months Ended
PENDING ACQUISITION (Details) - USD ($) $ in Thousands	Mar. 01, 2014	Mar. 31, 2014	Feb. 28, 2014
Business Acquisition [Line Items]
Payments to acquire businesses, gross	$ 585,000
Potential termination fee	$ 17,600
Business combination, acquisition related costs		$ 1,100
Apartments.com [Member]
Business Acquisition [Line Items]
Credit facility, collateral	The Company’s obligations under the Credit Facilities will be guaranteed (subject to certain exceptions) on a senior basis by each existing and subsequently acquired or organized direct or indirect wholly-owned restricted subsidiary of the Company (the “Subsidiary Guarantors”) and will be secured (subject to permitted liens and other agreed upon exceptions) on a first priority basis by a security interest in substantially all of the assets of CoStar and the Subsidiary Guarantors and a pledge of 100% (subject to certain exceptions) of the equity interests in each direct restricted subsidiary of Costar and each Subsidiary Guarantor.
New Term Loan [Member] \| Apartments.com [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity			$ 400,000
Term of loan (in years)	5 years
New Revolving Credit Facility [Member] \| Apartments.com [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity			$ 225,000
Term of loan (in years)	5 years
Notes Payable to Banks [Member] \| Apartments.com [Member]
Business Acquisition [Line Items]
Annual amortization, first year after closing (in percent)			5.00%
Annual amortization, second year after closing (in percent)			5.00%
Annual amortization, third year after closing (in percent)			5.00%
Annual amortization, fourth year after closing (in percent)			10.00%
Annual amortization, fifth year after closing (in percent)			15.00%

SUBSEQUENT EVENTS (Details) - USD ($) $ in Thousands				3 Months Ended	9 Months Ended
SUBSEQUENT EVENTS (Details) - USD ($) $ in Thousands	Apr. 03, 2014	Mar. 01, 2014	Feb. 16, 2012	Apr. 04, 2014	Jun. 30, 2012	Apr. 01, 2014	Mar. 31, 2014	Feb. 28, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Payments to acquire businesses, gross		$ 585,000
Line of credit facility, amount outstanding						$ 150,000			$ 0
LIBOR maturity period (in months)			1 month
Default interest rate per annum on overdue amounts (in percent)			2.00%
Maximum total leverage ratio after eight fiscal quarters (in percent)			250.00%
Debt issuance costs					$ 11,500
Debt issuance underwriting fees					9,200
Debt Issuance Legal Fees					$ 2,300
Capitalized debt issuance costs							$ 6,276		$ 6,542
Subsequent Event [Member]
Business Acquisition [Line Items]
Payments to acquire businesses, gross	$ 587,100
Post closing purchase price adjustments	$ 2,100
LIBOR maturity period (in months)	1 month
Default interest rate per annum on overdue amounts (in percent)						2.00%
Maximum first lien secured leverage ratio for first eight quarters after closing date (in percent)						400.00%
Maximum first lien secured leverage ratio after eight quarters after closing date (in percent)						350.00%
Maximum total leverage ratio for first eight quarters after closing date (in percent)						500.00%
Maximum total leverage ratio after eight fiscal quarters (in percent)						450.00%
Apartments.com [Member]
Business Acquisition [Line Items]
Credit facility, collateral		The Company’s obligations under the Credit Facilities will be guaranteed (subject to certain exceptions) on a senior basis by each existing and subsequently acquired or organized direct or indirect wholly-owned restricted subsidiary of the Company (the “Subsidiary Guarantors”) and will be secured (subject to permitted liens and other agreed upon exceptions) on a first priority basis by a security interest in substantially all of the assets of CoStar and the Subsidiary Guarantors and a pledge of 100% (subject to certain exceptions) of the equity interests in each direct restricted subsidiary of Costar and each Subsidiary Guarantor.
Apartments.com [Member] \| Subsequent Event [Member]
Business Acquisition [Line Items]
Credit facility, collateral	The obligations under the 2014 Credit Agreement are guaranteed by all material subsidiaries of CoStar and are secured by a lien on substantially all of the assets of CoStar and its material subsidiaries, in each case subject to certain exceptions, pursuant to security and guarantee documents entered into on the Closing Date.
Debt issuance costs				$ 10,400
Debt issuance underwriting fees				9,700
Debt Issuance Legal Fees				$ 700
Capitalized debt issuance costs						$ 10,200
New Term Loan [Member] \| Apartments.com [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity								$ 400,000
Term of loan (in years)		5 years
New Term Loan [Member] \| Apartments.com [Member] \| Subsequent Event [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity						400,000
Term of loan (in years)	5 years
New Revolving Credit Facility [Member]
Business Acquisition [Line Items]
Line of credit facility, amount outstanding							$ 0
New Revolving Credit Facility [Member] \| Apartments.com [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity								$ 225,000
Term of loan (in years)		5 years
New Revolving Credit Facility [Member] \| Apartments.com [Member] \| Subsequent Event [Member]
Business Acquisition [Line Items]
Debt instrument borrowing capacity						$ 225,000
Term of loan (in years)	5 years
Notes Payable to Banks [Member] \| Apartments.com [Member]
Business Acquisition [Line Items]
Annual amortization, first year after closing (in percent)								5.00%
Annual amortization, second year after closing (in percent)								5.00%
Annual amortization, third year after closing (in percent)								5.00%
Annual amortization, fourth year after closing (in percent)								10.00%
Annual amortization, fifth year after closing (in percent)								15.00%
CoStar Group [Member] \| Notes Payable to Banks [Member] \| Apartments.com [Member] \| Subsequent Event [Member]
Business Acquisition [Line Items]
Annual amortization, first year after closing (in percent)						5.00%
Annual amortization, second year after closing (in percent)						5.00%
Annual amortization, third year after closing (in percent)						5.00%
Annual amortization, fourth year after closing (in percent)						10.00%
Annual amortization, fifth year after closing (in percent)						15.00%
CoStar Group [Member] \| Maximum [Member] \| Swingline Loan [Member]
Business Acquisition [Line Items]
Revolving credit sub-facility for swing-line loans and issuances of letters of credit			$ 5,000
CoStar Group [Member] \| Maximum [Member] \| Swingline Loan [Member] \| Subsequent Event [Member]
Business Acquisition [Line Items]
Revolving credit sub-facility for swing-line loans and issuances of letters of credit						$ 10,000
CoStar Group [Member] \| Maximum [Member] \| Letter of Credit [Member]
Business Acquisition [Line Items]
Revolving credit sub-facility for swing-line loans and issuances of letters of credit			$ 10,000
CoStar Group [Member] \| Maximum [Member] \| Letter of Credit [Member] \| Subsequent Event [Member]
Business Acquisition [Line Items]
Revolving credit sub-facility for swing-line loans and issuances of letters of credit						$ 10,000
Federal Funds Rate [Member]
Business Acquisition [Line Items]
Basis spread on federal funds rate (in percent)			0.50%
Federal Funds Rate [Member] \| Subsequent Event [Member]
Business Acquisition [Line Items]
Basis spread on federal funds rate (in percent)	0.50%
LIBOR [Member]
Business Acquisition [Line Items]
Basis spread on federal funds rate (in percent)			2.00%
Debt instrument, basis spread on variable rate, one month interest period (in percent)			1.00%
Debt instrument, basis spread on variable rate, per annum (in percent)			1.00%
LIBOR [Member] \| Subsequent Event [Member]
Business Acquisition [Line Items]
Basis spread on federal funds rate (in percent)	2.00%
Debt instrument, basis spread on variable rate, one month interest period (in percent)						1.00%
Debt instrument, basis spread on variable rate, per annum (in percent)						1.00%

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2014	Dec. 31, 2013
Current assets:
Allowance for doubtful accounts	$ 3,857	$ 3,397

ORGANIZATION	3 Months Ended
ORGANIZATION	Mar. 31, 2014
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.

INCOME TAXES	3 Months Ended
INCOME TAXES	Mar. 31, 2014
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The income tax provision for the three months ended March 31, 2014 and 2013 reflects an effective tax rate of approximately 38% and 43%, respectively. 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.

ORGANIZATION (Details)	3 Months Ended
ORGANIZATION (Details)	Mar. 31, 2014 operating_segments
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of business segments (in segments)	2
Term of subscription-based license agreements (in years)	1 year

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, CAPITALIZED PRODUCT DEVELOPMENT AND DEBT ISSUANCE COSTS (Details) - USD ($)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Capitalized Product Development Costs [Abstract]
Finite-lived intangible assets, net	$ 137,168,000		$ 144,472,000
Amortization expense of capitalized product development costs	3,299,000	$ 4,125,000
Debt Issuance Cost [Abstract]
Capitalized debt issuance costs	6,276,000		6,542,000
Amortization of debt issuance costs	$ 710,000	747,000
Minimum [Member]
Capitalized Product Development Costs [Abstract]
Finite-lived intangible asset, useful life (in years)	3 years
Maximum [Member]
Capitalized Product Development Costs [Abstract]
Finite-lived intangible asset, useful life (in years)	5 years
Capitalized Product Development Costs [Member]
Capitalized Product Development Costs [Abstract]
Finite-lived intangible assets, net	$ 64,000		$ 111,000
Amortization expense of capitalized product development costs	$ 47,000	$ 47,000

GOODWILL (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
GOODWILL (Details) - USD ($) $ in Thousands	Mar. 31, 2014	Dec. 31, 2013
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 718,587	$ 718,078
Effect of foreign currency translation	237	509
Goodwill, ending balance	718,824	718,587
United States [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	692,639	692,639
Effect of foreign currency translation	0	0
Goodwill, ending balance	692,639	692,639
International [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	25,948	25,439
Effect of foreign currency translation	237	509
Goodwill, ending balance	$ 26,185	$ 25,948

INCOME TAXES (Details)	3 Months Ended
INCOME TAXES (Details)	Mar. 31, 2014	Mar. 31, 2013
Income Tax Disclosure [Abstract]
Effective income tax rate (in percent)	38.00%	43.00%