DEBT - Schedule of Total Interest Expense Recognized Related to the Convertible Notes (Details) - Convertible Debt - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Contractual interest expense	$ 10,467	$ 10,935	$ 8,961
Amortization of debt issuance costs	1,412	1,403	1,275
Amortization of debt discount	13,830	13,414	11,071
Total interest expense	$ 25,709	$ 25,752	$ 21,307