LONG-TERM DEBT - Schedule of Long-Term Debt (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Less: Debt issuance costs, net	$ (1,800,000)	$ (2,400,000)
Less: Current portion	(5,000,000)	0
Long-term debt, less current portion	258,247,000	242,656,000
Credit Facility
Debt Instrument [Line Items]
Senior secured term loans	20,000,000	0
Less: Debt issuance costs, net	(485,000)	0
Total Long-term debt	19,515,000	0
Less: Current portion	(5,000,000)	0
Long-term debt, less current portion	14,515,000	0
Senior secured term loans
Debt Instrument [Line Items]
Senior secured term loans	247,204,000	247,204,000
Less: Debt issuance costs, net	(1,812,000)	(2,389,000)
Less: Unamortized discount, net	(1,660,000)	(2,159,000)
Total Long-term debt	$ 243,732,000	$ 242,656,000