Document and Entity Information Document
Jun. 02, 2021
Cover [Abstract]  
Document Type 8-K
Document Period End Date Jun. 02, 2021
Entity Registrant Name COSTAR GROUP, INC.
Entity Central Index Key 0001057352
Amendment Flag false
Current Fiscal Year End Date --12-31
Entity Incorporation, State or Country Code DE
Entity File Number 0-24531
Entity Tax Identification Number 52-2091509
Entity Address, Address Line One 1331 L Street, NW,
Entity Address, City or Town Washington,
Entity Address, State or Province DC
Entity Address, Postal Zip Code 20005
City Area Code 202
Local Phone Number 346-6500
Written Communications false
Soliciting Material false
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Title of 12(b) Security Common Stock ($0.01 par value)
Trading Symbol CSGP
Security Exchange Name NASDAQ
Entity Emerging Growth Company false