DEBT - Summary of Interest Expense of Senior Notes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Amortization of debt discount and debt issuance costs	$ 21,877	$ 19,415	$ 17,673
Senior Notes
Debt Instrument [Line Items]
Contractual interest expense	38,242	44,212	54,722
Amortization of debt discount and debt issuance costs	3,589	2,631	2,261
Total interest expense	$ 41,831	$ 46,843	$ 56,983