XML 24 R1.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2
Cover page - USD ($)
$ in Billions
 12 Months Ended
Dec. 31, 2019
Feb. 21, 2020
Jun. 28, 2019
Cover page.      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2019    
Document Transition Report false    
Entity File Number 0-24531    
Entity Registrant Name COSTAR GROUP INC    
Entity Central Index Key 0001057352    
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2019    
Document Fiscal Period Focus FY    
Amendment Flag false    
Entity Incorporation, State or Country Code DE    
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    
Title of 12(b) Security Common Stock ($0.01 par value)    
Trading Symbol CSGP    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Small Business Entity false    
Emerging Growth false    
Entity Shell Company false    
Public Float     $ 20
Entity Common Stock, Shares Outstanding   36,644,734  
Documents Incorporated by Reference
Portions of the registrant’s definitive proxy statement, which is expected to be filed with the Securities and Exchange Commission within 120 days after the end of the registrant’s fiscal year ended December 31, 2019, are incorporated by reference into Part III of this Report.