DEBT - Summary of Cash Flow Hedges (Details) - Designated as Hedging Instrument - Interest rate swaps - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Cash flow hedge derivatives, gross liability	$ 7,604	$ 13,237
Other non-current assets
Derivatives, Fair Value [Line Items]
Cash flow hedge derivatives, gross asset	228	0
Other accrued liabilities
Derivatives, Fair Value [Line Items]
Cash flow hedge derivatives, gross liability	4,612	4,774
Other long-term liabilities
Derivatives, Fair Value [Line Items]
Cash flow hedge derivatives, gross liability	2,992	8,463
Accumulated other comprehensive loss, net of tax
Derivatives, Fair Value [Line Items]
Accumulated other comprehensive loss, interest rate swaps	(7,568)	(13,434)
Accumulated other comprehensive loss, interest rate swaps, tax provision	538	1,917
Accumulated other comprehensive loss, net of tax	$ (7,030)	$ (11,517)