v3.25.2
REVENUE FROM CONTRACTS WITH CUSTOMERS - Disaggregated Revenue (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Disaggregation of Revenue [Line Items]        
Revenues $ 781.3 $ 677.8 $ 1,513.5 $ 1,334.2
North America        
Disaggregation of Revenue [Line Items]        
Revenues 744.0 643.8 1,441.4 1,267.1
International        
Disaggregation of Revenue [Line Items]        
Revenues 37.3 34.0 72.1 67.1
CoStar        
Disaggregation of Revenue [Line Items]        
Revenues 270.9 253.0 536.0 503.3
CoStar | North America        
Disaggregation of Revenue [Line Items]        
Revenues 251.6 237.1 499.2 472.8
CoStar | International        
Disaggregation of Revenue [Line Items]        
Revenues 19.3 15.9 36.8 30.5
Information Services        
Disaggregation of Revenue [Line Items]        
Revenues 39.3 33.4 79.1 66.4
Information Services | North America        
Disaggregation of Revenue [Line Items]        
Revenues 35.7 27.9 71.7 55.3
Information Services | International        
Disaggregation of Revenue [Line Items]        
Revenues 3.6 5.5 7.4 11.1
Multifamily        
Disaggregation of Revenue [Line Items]        
Revenues 292.3 264.2 574.8 519.0
Multifamily | North America        
Disaggregation of Revenue [Line Items]        
Revenues 292.3 264.2 574.8 519.0
Multifamily | International        
Disaggregation of Revenue [Line Items]        
Revenues 0.0 0.0 0.0 0.0
LoopNet        
Disaggregation of Revenue [Line Items]        
Revenues 75.7 69.8 148.5 138.9
LoopNet | North America        
Disaggregation of Revenue [Line Items]        
Revenues 72.6 67.2 142.6 133.6
LoopNet | International        
Disaggregation of Revenue [Line Items]        
Revenues 3.1 2.6 5.9 5.3
Residential        
Disaggregation of Revenue [Line Items]        
Revenues 28.4 26.2 55.6 44.8
Residential | North America        
Disaggregation of Revenue [Line Items]        
Revenues 17.1 16.2 33.6 24.6
Residential | International        
Disaggregation of Revenue [Line Items]        
Revenues 11.3 10.0 22.0 20.2
Other Revenues        
Disaggregation of Revenue [Line Items]        
Revenues 74.7 31.2 119.5 61.8
Other Revenues | North America        
Disaggregation of Revenue [Line Items]        
Revenues 74.7 31.2 119.5 61.8
Other Revenues | International        
Disaggregation of Revenue [Line Items]        
Revenues $ 0.0 $ 0.0 $ 0.0 $ 0.0