ALLOWANCE FOR CREDIT LOSSES (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 13,374	$ 15,110
Current-period provision for expected credit losses	13,468	7,797
Write-offs charged against the allowance, net of recoveries and other	(17,508)	(9,858)
Ending balance	9,334	13,049
CoStar
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	5,380	5,531
Current-period provision for expected credit losses	7,089	3,932
Write-offs charged against the allowance, net of recoveries and other	(8,917)	(3,933)
Ending balance	3,552	5,530
Information Services
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,820	2,739
Current-period provision for expected credit losses	(703)	(257)
Write-offs charged against the allowance, net of recoveries and other	(198)	(518)
Ending balance	919	1,964
Multifamily
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	3,393	4,387
Current-period provision for expected credit losses	4,032	2,167
Write-offs charged against the allowance, net of recoveries and other	(4,362)	(3,779)
Ending balance	3,063	2,775
LoopNet
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,968	1,667
Current-period provision for expected credit losses	3,000	1,955
Write-offs charged against the allowance, net of recoveries and other	(4,031)	(1,628)
Ending balance	937	1,994
Other Marketplaces
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	813	786
Current-period provision for expected credit losses	50	0
Write-offs charged against the allowance, net of recoveries and other	0	0
Ending balance	$ 863	$ 786