SUBSEQUENT EVENTS	9 Months Ended
Sep. 30, 2021
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTSBureauxLocauxOn October 1, 2021, CoStar UK Limited ("CoStar UK"), a wholly-owned subsidiary of the Company, purchased from M.A.J.E Marketing & Stratégie and an individual all of the outstanding equity interests in ComReal Info, a French société par actions simplifiéee, for €35 million, $41 million equivalent, in cash subject to customary working capital and other post-closing adjustments. Based in Paris, ComReal Info owns and operates BureauxLocaux, a leading commercial real estate digital marketplace in France. The Company used cash on hand to finance the acquisition and expects to record most of the purchase price to identifiable intangible assets and goodwill

The entire disclosure for significant events or transactions that occurred after the balance sheet date through the date the financial statements were issued or the date the financial statements were available to be issued. Examples include: the sale of a capital stock issue, purchase of a business, settlement of litigation, catastrophic loss, significant foreign exchange rate changes, loans to insiders or affiliates, and transactions not in the ordinary course of business.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 855
-URI http://asc.fasb.org/topic&trid=2122774

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 855
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6842918&loc=SL6314017-165662

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