DEBT - 5.00% Convertible Senior Notes Due 2024 (Details)			3 Months Ended		12 Months Ended
	Apr. 08, 2020 USD ($)	Aug. 13, 2019 USD ($) trading_day $ / shares	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Feb. 19, 2020 USD ($)
Debt Instrument [Line Items]
Debt instrument, unamortized discount					$ 16,000	$ 70,699,000
(Loss) Gain on debt extinguishment					(56,113,000)	26,385,000
Liability Component [Abstract]
Total principal amount					84,118,000	427,500,000
Unamortized discount of the liability component					(16,000)	(70,699,000)
Unamortized debt issuance costs					0	(5,543,000)
Carrying value					84,102,000	351,258,000
Interest Expense [Abstract]
Amortization of debt discount and debt issuance costs					5,680,000	23,764,000
Interest expense					6,870,000
Convertible debt
Debt Instrument [Line Items]
(Loss) Gain on debt extinguishment					(47,880,000)	26,385,000
Reacquisition of equity component					19,532,000
Interest Expense [Abstract]
Stated coupon interest					637,000	6,708,000
Amortization of debt discount and debt issuance costs					1,550,000	15,398,000
Interest expense					$ 2,187,000	22,106,000
Convertible Senior Notes, 5.0% | Convertible debt
Debt Instrument [Line Items]
Interest rate		5.00%			5.00%
Par value of debt		$ 120,000,000.0
Conversion rate of common stock		0.3235198
Conversion price (in dollars per share) | $ / shares		$ 3.09
Observation period		40 days
Stock price trigger		150.00%
Trading days, number (trading day) | trading_day		20
Consecutive trading days, period (trading day) | trading_day		30
Redemption price, percentage	99.50%	100.00%
Debt instrument, debt default, percent of principal and unpaid interest due and payable immediately		100.00%
Effective interest rate		17.82%
Estimated fair value of debt		$ 98,400,000
Liability component of debt		65,800,000
Debt instrument, unamortized discount		54,200,000				51,701,000
Debt instrument, unamortized discount, fair value		21,600,000
Equity component of debt		32,600,000
Debt and equity issuance costs, net		4,300,000
Debt issuance costs, net		2,900,000
Repurchased aggregate principal amount	$ 34,500,000						$ 85,500,000
(Loss) Gain on debt extinguishment			$ (12,400,000)	$ (21,300,000)
Reacquisition of equity component			$ 2,700,000	$ 16,800,000
Liability Component [Abstract]
Total principal amount					$ 0	120,000,000
Unamortized discount of the liability component		$ (54,200,000)				(51,701,000)
Unamortized debt issuance costs						(2,796,000)
Carrying value						65,503,000
Interest Expense [Abstract]
Stated coupon interest					1,090,000	2,250,000
Amortization of debt discount and debt issuance costs					1,273,000	2,583,000
Interest expense					$ 2,363,000	$ 4,833,000