SUBSEQUENT EVENTS - Narrative (Details) - USD ($) $ in Thousands					1 Months Ended		12 Months Ended
	Feb. 13, 2020	Feb. 06, 2020	Jan. 10, 2020	Dec. 04, 2017	Nov. 30, 2017	Apr. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2021	Dec. 31, 2020	Feb. 19, 2020
Subsequent events
Payment of a prepayment fee							$ 30,000	$ 0	$ 7,400
Senior Notes
Subsequent events
Payment of a prepayment fee				$ 400	$ 400	$ 4,000			$ 4,400
Subsequent Event | Eolas Pharma Teoranta
Subsequent events
Recover of accounts receivable		$ 2,000
Subsequent Event | Senior Notes
Subsequent events
Repurchased aggregate principal amount	$ 162,500
Payment of a prepayment fee	4,900
Payment debt exit fees	4,400
Subsequent Event | 2021 Notes and 2024 Notes | Convertible debt
Subsequent events
Repurchased aggregate principal amount												$ 188,000
Subsequent Event | Gralise | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Subsequent events
Consideration received, including base purchase price and inventory adjustment			$ 78,600
Consideration received, base purchase price			75,000
Consideration received, inventory adjustment upon disposal			$ 3,600
Consideration receivable as percentage of net sales after closing			75.00%
Threshold for consideration receivable on net sales after closing			$ 70,000
Subsequent Event | NUCYNTA | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Subsequent events
Net proceeds received	368,000
Proceeds from divestiture of businesses	375,000
Proceeds from divestiture of businesses, inventory amount	6,000
Payment for royalties, divested business	$ 13,000
Subsequent Event | NUCYNTA | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Forecast | Third-Party Consent Agreement
Subsequent events
Lump sum payments obligation										$ 4,500	$ 4,500
Subsequent Event | Long-acting Cosyntropin Development Partnership | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Subsequent events
Contingent consideration		$ 10,000