The amount of goodwill recognized as of the acquisition date.

No definition available.

Name:	csgp_BusinessCombinationRecognizedGoodwillAcquired
Namespace Prefix:	csgp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The number of distinct intangible assets identified.

+ References

No definition available.

+ Details

Name:	csgp_NumberOfDistinctIntangibleAsset
Namespace Prefix:	csgp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Term of Consent Order Public Comment Period

+ References

No definition available.

+ Details

Name:	csgp_TermOfConsentOrderPublicCommentPeriod
Namespace Prefix:	csgp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16265-109275

+ Details

Name:	us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of voting equity interests acquired at the acquisition date in the business combination.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of goodwill arising from a business combination that is expected to be deductible for tax purposes.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=7488404&loc=d3e6927-128479

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 25

-Paragraph 23

-URI http://asc.fasb.org/extlink&oid=21917927&loc=d3e1043-128460

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
Period Type:	duration

- Definition

The difference between the book value and the sale price of other nonspecific investments. This element is used when other, more specific, elements are not appropriate. This element refers to the gain (loss) included in earnings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow from the sale of investment projects held by an entity in hopes of getting a future return or interest from it.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585

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ACQUISITIONS (Details) (USD $)		0 Months Ended	3 Months Ended		9 Months Ended			9 Months Ended	0 Months Ended	9 Months Ended	0 Months Ended
ACQUISITIONS (Details) (USD $)	Apr. 26, 2012	May 03, 2012 LoopNet [Member]	Sep. 30, 2013 LoopNet [Member]	Sep. 30, 2012 LoopNet [Member]	Sep. 30, 2013 LoopNet [Member]	Sep. 30, 2012 LoopNet [Member]	Apr. 30, 2012 LoopNet [Member] distinct_intangible_asset	Sep. 30, 2013 Acquired Customer Base [Member]	Apr. 30, 2012 Acquired Customer Base [Member] LoopNet [Member]	Sep. 30, 2013 Acquired Database Technology [Member]	Apr. 30, 2012 Acquired Database Technology [Member] LoopNet [Member]
Business Acquisition [Line Items]
Percentage of outstanding stock controlled by compnay							100.00%
Distinct intangible asset (in intangible asset)							1
Estimated useful life of acquired assets								10 years	10 years	5 years	5 years
Business combination, recognized goodwill acquired							$ 625,174,000
Goodwill tax deductible amount							0
Incurred acquisition-related costs			0	0	0	5,200,000
Term of consent order public comment period	30 days
Proceeds from sale of Xcelignet		4,200,000
Gain on sale of Xceligent		$ 0