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DEBT - Summary of Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2020	May 20, 2020	Dec. 31, 2019	Aug. 13, 2019	Sep. 09, 2014
Debt Instrument [Line Items]
Total principal amount	$ 84,118		$ 427,500
Unamortized debt discounts	(16)		(70,699)
Unamortized debt issuance costs	0		(5,543)
Carrying value	84,102		351,258
Less: current portion of long-term debt	(11,942)		(80,000)
Long-term debt	72,160		271,258
Senior Notes
Debt Instrument [Line Items]
Total principal amount	$ 0		162,500
Unamortized debt discounts			(4,035)
Unamortized debt issuance costs			(2,022)
Carrying value			156,443
Senior Notes \| 13% Senior Secured Note due 2024
Debt Instrument [Line Items]
Interest rate	13.00%	13.00%
Total principal amount	$ 80,250		0
Senior Notes \| Royalty rights obligation
Debt Instrument [Line Items]
Total principal amount	$ 3,533		0
Convertible debt \| 2.50% Convertible Notes due 2021
Debt Instrument [Line Items]
Interest rate	2.50%				2.50%
Total principal amount	$ 335		145,000
Unamortized debt discounts	0		(14,963)		$ (119,000)
Unamortized debt issuance costs	0		(725)
Carrying value	$ 335		129,312
Convertible debt \| 5.0% Convertible Notes debt 2024
Debt Instrument [Line Items]
Interest rate	5.00%			5.00%
Total principal amount	$ 0		120,000
Unamortized debt discounts			(51,701)	$ (54,200)
Unamortized debt issuance costs			(2,796)
Carrying value			$ 65,503