Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266

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Period Type:	instant

- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267

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Balance Type:	debit
Period Type:	duration

- Definition

Amount of increase (decrease) of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=108376223&loc=d3e13816-109267

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- Details

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- Details

Name:	us-gaap_BusinessAcquisitionAxis=csgp_ReallaLtdMember
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- Details

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GOODWILL (Narrative) (Details) $ in Thousands, £ in Millions				6 Months Ended	12 Months Ended
	Nov. 08, 2018 USD ($)	Oct. 12, 2018 GBP (£)	Oct. 12, 2018 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Feb. 21, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Goodwill				$ 1,617,853	$ 1,611,535		$ 1,283,457
Goodwill acquired				6,449	$ 329,938
Off Campus Partners [Member]
Business Acquisition [Line Items]
Goodwill				8,000
ForRent, Division Of DE Holdings, Inc. [Member]
Business Acquisition [Line Items]
Goodwill						$ 266,595
Realla Ltd [Member]
Business Acquisition [Line Items]
Goodwill acquired		£ 8	$ 10,000
Cozy Services Ltd [Member]
Business Acquisition [Line Items]
Goodwill acquired	$ 52,000			53,000
Goodwill increase (decrease)				$ (1,000)