LONG-TERM OBLIGATIONS - Summary of Long-Term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Principal amount	$ 217,700	$ 245,700
Deferred debt issuance costs	(2,700)	(3,500)
Long-term obligations, including current portion	215,000	242,200
Current portion of long-term obligations	(10,496)	(9,927)
Long-term obligations, less current portion	204,511	232,256
Term Loan [Member] \| One Hundred Seventy Five Million Term Loan Facility [Member]
Debt Instrument [Line Items]
Principal amount	164,100	171,700
Revolving Credit Facility [Member] \| Five Hundred Fifty Million Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Principal amount	51,000	70,000
Promissory Notes [Member]
Debt Instrument [Line Items]
Principal amount	0	600
Finance Leases [Member]
Debt Instrument [Line Items]
Principal amount	$ 2,600	$ 3,400

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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