LONG-TERM DEBT - Net Interest Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2020	Jun. 30, 2019
Interest Expense, Debt [Abstract]
Interest expense	$ 86,579	$ 100,757	$ 101,497
Amortization of deferred financing costs	3,981	3,085	3,189
Amortization of original issue discount (premium) of senior notes	(3,395)	(2,928)	(2,862)
Interest income and other investment income	(69)	(811)	(703)
Total net interest expense	$ 87,096	$ 100,103	$ 101,121
Weighted average interest rate under Credit Facility	2.60%	4.30%
Notional amount				$ 560,000	$ 560,000