DEBT - Narrative (Details) $ / shares in Units, shares in Thousands						1 Months Ended				3 Months Ended		12 Months Ended
	Feb. 13, 2020 USD ($)	Aug. 13, 2019 USD ($) trading_day $ / shares shares	Dec. 04, 2017 USD ($)	Apr. 02, 2015 USD ($)	Sep. 09, 2014 USD ($) trading_day $ / shares	Jan. 31, 2020 USD ($)	Jan. 31, 2019 USD ($)	Nov. 30, 2017 USD ($)	Apr. 30, 2017 USD ($)	Dec. 31, 2019 USD ($) $ / shares	Sep. 30, 2019 USD ($) shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2015 USD ($)	Aug. 31, 2019 USD ($)
Debt Instrument [Line Items]
Debt issuance costs												$ 4,268,000	$ 0	$ 0
Payment of a prepayment fee												30,000,000	0	7,400,000
Gain on prepayment of debt												26,385,000	0	(5,938,000)
Amortization of debt discount and debt issuance costs												$ 23,764,000	$ 21,877,000	19,415,000
Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount of notes issued				$ 575,000,000.0
Proceeds from the issuance of debt				$ 562,000,000
Debt issuance costs															$ 500,000
Effective interest rate										11.83%		11.83%	12.15%
Amount of debt prepaid			$ 10,000,000.0					$ 10,000,000	$ 100,000,000
Payment of a prepayment fee			400,000					$ 400,000	$ 4,000,000					4,400,000
Gain on prepayment of debt														(5,900,000)
Unamortized balances of debt discount and debt issuance costs														1,500,000
Threshold limit of asset dispositions which is required to make mandatory prepayments on senior notes												$ 10,000,000.0
Amendment fee			$ 3,000,000				$ 3,200,000
Principal payments, 2020										$ 80,000,000		80,000,000
Principal payments, 2021										82,500,000		82,500,000
Debt instrument, unamortized discount										$ 4,035,000		4,035,000	$ 2,541,000
Amortization of debt discount and debt issuance costs												$ 5,783,000	3,589,000	2,631,000
Senior Notes | Period One
Debt Instrument [Line Items]
Prepayment premium, percent							3.00%
Senior Notes | Period Two
Debt Instrument [Line Items]
Prepayment premium, percent							1.00%
Senior Notes | Three month LIBOR
Debt Instrument [Line Items]
Basis spread				9.75%
Interest rate through third anniversary				11.95%
Interest rate after third anniversary				12.95%
Senior Notes | Three month LIBOR | Minimum
Debt Instrument [Line Items]
Interest rate				1.00%
Senior Notes | NUCYNTA
Debt Instrument [Line Items]
Proceeds from the issuance of debt				$ 550,000,000
Convertible debt
Debt Instrument [Line Items]
Interest rate										2.50%		2.50%
Debt instrument, unamortized discount										$ 14,963,000		$ 14,963,000	54,521,000
Amortization of debt discount and debt issuance costs												$ 15,398,000	$ 18,288,000	$ 16,784,000
Convertible Senior Notes, 2.5% | Convertible debt
Debt Instrument [Line Items]
Aggregate principal amount of notes issued					$ 345,000,000.0						$ 145,000,000.0
Interest rate					2.50%
Effective interest rate					9.34%
Amount of debt prepaid		$ 200,000,000									200,000,000
Gain on prepayment of debt											26,400,000
Unamortized balances of debt discount and debt issuance costs											18,900,000
Debt instrument, maximum borrowing capacity, in connection with debt exchange																$ 30,000,000.0
Debt instrument, exit fee due, if circumstances met																$ 4,400,000
Net proceeds from debt offering					$ 334,200,000
Underwriting discount					10,400,000
Offering expenses					$ 400,000
Trading days, number (trading day) | trading_day					20
Consecutive trading days, period (trading day) | trading_day					30
Stock price trigger (in dollars per share) | $ / shares					$ 25.01
Stock price trigger					130.00%					130.00%
Conversion price (in dollars per share) | $ / shares					$ 19.24					$ 19.24		$ 19.24
Business days, period					5 days
Consecutive trading-day period					5 days
Principal amount					$ 1,000
Maximum product of the closing sale price of shares of the Company's common stock and the applicable conversion rate for such trading day (less than)					98.00%
Conversion rate of common stock					0.0519852
Observation period					40 days
Liability component of debt					$ 226,000,000
Debt instrument, unamortized discount					119,000,000
Equity component of debt					73,300,000						112,800,000
Extinguishment of debt, cash paid		30,000,000									30,000,000
Reacquisition of equity component of debt, net of tax											6,200,000	$ (4,763,000)
Amortization of debt discount and debt issuance costs											26,100,000
Decrease in carrying amount of equity component											$ 6,200,000
Convertible Senior Notes, 5.0% | Convertible debt
Debt Instrument [Line Items]
Aggregate principal amount of notes issued		$ 120,000,000.0
Interest rate		5.00%
Effective interest rate		17.82%
Trading days, number (trading day) | trading_day		20
Consecutive trading days, period (trading day) | trading_day		30
Stock price trigger		150.00%
Conversion price (in dollars per share) | $ / shares		$ 3.09
Principal amount		$ 1,000
Conversion rate of common stock		0.3235198
Observation period		40 days
Liability component of debt		$ 65,800,000
Debt instrument, unamortized discount		54,200,000								$ 51,701,000		51,701,000
Equity component of debt		32,600,000
Reacquisition of equity component of debt, net of tax												23,999,000
Amortization of debt discount and debt issuance costs												2,583,000
Debt instrument, fundamental change occurred, principal amount, cash repurchase requirement, if circumstances met		1,000
Debt instrument, fundamental change occurred, principal amount multiple, cash repurchase requirement, if circumstances met		$ 1,000
Debt instrument, fundamental change occurred, principal amount percentage, cash repurchase requirement, if circumstances met		100.00%
Redemption price, percentage		100.00%
Debt instrument, debt default, percent of principal and unpaid interest due and payable immediately		100.00%
Estimated fair value of debt		$ 98,400,000
Debt instrument, unamortized discount, fair value		21,600,000
Debt and equity issuance costs, net		4,300,000
Debt issuance costs, net		$ 2,900,000
Additional Paid-In Capital | Convertible Senior Notes, 2.5% | Convertible debt
Debt Instrument [Line Items]
Equity issuance costs					$ 3,700,000
Reacquisition of equity component of debt, net of tax												(4,763,000)
Additional Paid-In Capital | Convertible Senior Notes, 5.0% | Convertible debt
Debt Instrument [Line Items]
Reacquisition of equity component of debt, net of tax												$ 23,999,000
Common Stock
Debt Instrument [Line Items]
Stock issued during period, shares, new issues | shares		15,800									15,800	15,817
Beneficial Owner | Convertible Senior Notes, 2.5% | Convertible debt
Debt Instrument [Line Items]
Aggregate principal amount of notes issued		$ 22,000,000
Payment of a prepayment fee		3,500,000
Beneficial Owner | Convertible Senior Notes, 5.0% | Convertible debt
Debt Instrument [Line Items]
Aggregate principal amount of notes issued		$ 13,200,000
Beneficial Owner | Common Stock
Debt Instrument [Line Items]
Stock issued during period, shares, new issues | shares		1,700
Subsequent Event | Senior Notes
Debt Instrument [Line Items]
Payment of a prepayment fee	$ 4,900,000
Prepayment of principal						$ 60,500,000