DEBT - Narrative (Details)				1 Months Ended		3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 04, 2017 USD ($)	Apr. 02, 2015 USD ($)	Sep. 09, 2014 USD ($) trading_day $ / shares	Nov. 30, 2017 USD ($)	Apr. 30, 2017 USD ($)	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2015 USD ($)	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Payment of a prepayment fee								$ 0	$ 7,400,000	$ 5,000,000
Loss on prepayment of debt								$ 0	$ 5,938,000	$ 5,777,000
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
Interest rate						2.50%		2.50%
Effective interest rate						12.15%		12.15%	11.09%
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
Loss on prepayment of debt									5,900,000
Unamortized balances of debt discount and debt issuance costs									1,500,000
Principal amount of the Convertible Notes						$ 282,500,000		$ 282,500,000	365,000,000
Threshold limit to repay principal amount outstanding in full								100,000,000.0
Threshold limit of asset dispositions which is required to make mandatory prepayments on senior notes								10,000,000.0
Amendment fee	$ 3,000,000
Principal payments						120,000,000		120,000,000
Senior Notes | Period One
Debt Instrument [Line Items]
Prepayment premium	4.00%
Senior Notes | Period Two
Debt Instrument [Line Items]
Prepayment premium	0.00%
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]
Aggregate principal amount of notes issued			$ 345,000,000.0			$ 345,000,000		$ 345,000,000
Interest rate			2.50%			2.50%		2.50%
Effective interest rate			9.34%
Principal amount of the Convertible Notes						$ 345,000,000		$ 345,000,000	$ 345,000,000
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
Equity component of debt			119,000,000
Equity component of convertible debt issued, net of tax			73,300,000
Convertible debt | Additional Paid-In Capital
Debt Instrument [Line Items]
Equity issuance costs			$ 3,700,000