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Period Type:	instant

Share Based Compensation Exercisable Range [Abstract]

No definition available.

Name:	csgp_ShareBasedCompensationExercisableRangeAbstract
Namespace Prefix:	csgp_
Data Type:	xbrli:stringItemType
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The range of exercise prices for purposes of disclosing stock option canceled or expired and other required information pertaining to stock option plans in the customized range.

No definition available.

Name:	csgp_SharebasedCompensationSharesCanceledorExpiredUnderStockOptionPlansExercisePriceRange
Namespace Prefix:	csgp_
Data Type:	num:perShareItemType
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The range of exercise prices for purposes of disclosing stock option exercised and other required information pertaining to stock option plans in the customized range.

No definition available.

Name:	csgp_SharebasedCompensationSharesExercisedUnderStockOptionPlansExercisePriceRange
Namespace Prefix:	csgp_
Data Type:	num:perShareItemType
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The range of exercise prices for purposes of disclosing stock option granted and other required information pertaining to stock option plans in the customized range.

No definition available.

Name:	csgp_SharebasedCompensationSharesGrantedUnderStockOptionPlansExercisePriceRange
Namespace Prefix:	csgp_
Data Type:	num:perShareItemType
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The minimum and maximm exercise price range as of the balance sheet date at which grantees could acquire the underlying shares with respect to all outstanding stock options which are in the customized range of exercise prices.

No definition available.

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Namespace Prefix:	csgp_
Data Type:	num:perShareItemType
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- References

No definition available.

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract
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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Data Type:	num:perShareItemType
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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Data Type:	xbrli:sharesItemType
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Weighted average price of options that were either forfeited or expired.

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Data Type:	num:perShareItemType
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Net number of share options (or share units) granted during the period.

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Data Type:	xbrli:sharesItemType
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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Number of options outstanding, including both vested and non-vested options.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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Data Type:	xbrli:stringItemType
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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
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Period Type:	instant

Weighted average price at which option holders acquired shares when converting their stock options into shares.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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

Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
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Period Type:	duration

Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

Number of share options (or share units) exercised during the current period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(2)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644