DEBT - Summary of Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Long-term Debt, Unclassified [Abstract]
Stated coupon interest	$ 2,454	$ 2,938	$ 7,624	$ 7,714
Amortization of debt discount, and royalty rights	41	103	159	5,614
Total interest expense	$ 2,495	$ 3,041	$ 7,783	$ 13,328