DEBT - Narrative (Details) $ / shares in Units, shares in Millions						3 Months Ended
	Feb. 19, 2020 USD ($)	Feb. 13, 2020 USD ($)	Aug. 13, 2019 USD ($) shares	Apr. 02, 2015 USD ($)	Sep. 09, 2014 USD ($)	Mar. 31, 2020 USD ($) $ / shares	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Mar. 11, 2020 USD ($)
Debt Instrument [Line Items]
Loss on extinguishment of convertible notes						$ 31,608,000		$ 0
Accretion of debt discount and debt issuance costs						$ 5,387,000		$ 6,164,000
Common Stock
Debt Instrument [Line Items]
Extinguishment of debt, shares issued (in shares) | shares			15.8
Senior Notes
Debt Instrument [Line Items]
Aggregate principal amount				$ 575,000,000.0
Proceeds from the issuance of debt				$ 562,000,000.0
Effective interest rate						11.65%		12.54%
Repurchased aggregate principal amount		$ 162,500,000
Payment of debt extinguishment		4,900,000				$ 171,775,000		$ 28,249,000
Payment accrued exit fees		$ 4,400,000
Loss on extinguishment of convertible notes						8,200,000
Debt prepayment fee						4,900,000
Unamortized balances of debt discount and debt issuance costs						3,300,000
Accretion of debt discount and debt issuance costs						2,699,000		1,357,000
Senior Notes | Three month LIBOR
Debt Instrument [Line Items]
Basis spread				9.75%
Interest rate through third anniversary of purchase date				11.95%
Interest rate after third anniversary of purchase date				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				$ 550,000,000.0
Convertible debt
Debt Instrument [Line Items]
Payment of debt extinguishment						188,060,000		0
Reacquisition in additional paid-in capital, equity component						16,814,000
Convertible debt | 2.5% Convertible Notes debt 2021
Debt Instrument [Line Items]
Aggregate principal amount	$ 42,500,000				$ 345,000,000.0		$ 145,000,000.0
Interest rate					2.50%
Repurchased aggregate principal amount	102,500,000
Loss on extinguishment of convertible notes						10,300,000
Unamortized balances of debt discount and debt issuance costs	4,300,000						18,900,000
Debt extinguishment, amount			$ 200,000,000.0				200,000,000.0
Extinguishment of debt, cash paid			30,000,000.0
Reduction in carrying amount of equity component	300,000						6,200,000
Accretion of debt discount and debt issuance costs	10,300,000					1,469,000	26,100,000	$ 4,807,000
Carrying amount of equity component	112,500,000						$ 112,800,000
Reacquisition in additional paid-in capital, equity component						$ 300,000
Stock price trigger						130.00%
Conversion price (in dollars per share) | $ / shares						$ 19.24
Business days, period					5 days
Consecutive trading-day period					5 days
Conversion ratio					0.0519852
Convertible debt | 5.0% Convertible Notes debt 2024
Debt Instrument [Line Items]
Aggregate principal amount	34,500,000		$ 120,000,000.0
Interest rate			5.00%
Repurchased aggregate principal amount	85,500,000
Loss on extinguishment of convertible notes						$ 21,300,000
Unamortized balances of debt discount and debt issuance costs	15,400,000
Reduction in carrying amount of equity component						16,500,000
Accretion of debt discount and debt issuance costs	38,100,000					1,219,000
Carrying amount of equity component	16,100,000
Reacquisition in additional paid-in capital, equity component						$ 16,800,000
Conversion ratio			0.3235198
Convertible debt | Convertible Senior Notes 2.5% And Convertible Senior Notes 5.0%
Debt Instrument [Line Items]
Repurchased aggregate principal amount	$ 188,000,000.0
Tender offer to repurchase debt									$ 77,000,000.0