ALLOWANCE FOR CREDIT LOSSES (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 12,195	$ 13,374
Current-period provision (release) for expected credit losses	13,938	6,890
Write-offs charged against the allowance, net of recoveries and other	(11,091)	(10,626)
Ending balance	15,042	9,638
CoStar
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	4,510	5,380
Current-period provision (release) for expected credit losses	8,781	3,422
Write-offs charged against the allowance, net of recoveries and other	(8,072)	(4,708)
Ending balance	5,219	4,094
Information Services
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,051	1,820
Current-period provision (release) for expected credit losses	504	(1,063)
Write-offs charged against the allowance, net of recoveries and other	(104)	9
Ending balance	1,451	766
Multifamily
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	4,347	3,393
Current-period provision (release) for expected credit losses	2,092	2,676
Write-offs charged against the allowance, net of recoveries and other	(910)	(2,849)
Ending balance	5,529	3,220
LoopNet
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,396	1,968
Current-period provision (release) for expected credit losses	2,603	1,805
Write-offs charged against the allowance, net of recoveries and other	(2,005)	(3,078)
Ending balance	1,994	695
Other Marketplaces
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	891	813
Current-period provision (release) for expected credit losses	(42)	50
Write-offs charged against the allowance, net of recoveries and other	0	0
Ending balance	$ 849	$ 863