SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Rollforward of Allowance for Doubtful Accounts (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for doubtful accounts, beginning of period	$ 11.2	$ 16.9	$ 12.9	$ 11.2
Current period bad debt expense	1.2	0.2	1.2	7.1
Write-offs, net of recoveries	(1.1)	(1.3)	(2.8)	(2.5)
Allowance for doubtful accounts, end of period	$ 11.3	$ 15.8	$ 11.3	$ 15.8