v3.26.1
Cover page - shares
3 Months Ended
Mar. 31, 2026
Apr. 27, 2026
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Mar. 31, 2026  
Document Transition Report false  
Entity File Number 0-24531  
Entity Registrant Name CoStar Group, Inc.  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 52-2091509  
Entity Address, Address Line One 1201 Wilson Blvd  
Entity Address, City or Town Arlington  
Entity Address, State or Province VA  
Entity Address, Postal Zip Code 22209  
City Area Code (202)  
Local Phone Number 346-6500  
Title of 12(b) Security Common Stock ($0.01 par value)  
Trading Symbol CSGP  
Security Exchange Name NASDAQ  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   408,355,715
Entity Central Index Key 0001057352  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q1  
Amendment Flag false