LONG-TERM DEBT - Components of Convertible Debt Interest Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Amortization of debt discount and issuance costs	$ 8,829	$ 7,695	$ 7,022
Total interest expense	29,818	29,713	$ 30,875
Convertible debt
Debt Instrument [Line Items]
Coupon interest	11,329	11,500
Amortization of debt discount and issuance costs	6,938	6,435
Total interest expense	$ 18,267	$ 17,935
Effective interest rate	9.12%	9.12%