DEBT (Details)			1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	Apr. 02, 2015 USD ($)	Sep. 09, 2014 USD ($) item $ / shares	Nov. 30, 2017 USD ($)	Apr. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2015 USD ($)
Debt
Payment of a prepayment fee								$ 4,000,000
Loss on prepayment of debt						$ (5,364,000)		(5,364,000)
Carrying amounts of the liability component
Net carrying amount of the Senior Notes					$ 196,581,000		$ 196,581,000			$ 274,720,000
Interest expense incurred
Amortization of debt discount and debt issuance costs							10,808,000	$ 9,411,000
Net carrying amount of the liability component					278,457,000		278,457,000			269,510,000
Senior Notes
Debt
Aggregate principal amount of notes issued	$ 575,000,000				$ 307,500,000		$ 307,500,000
Proceeds from the issuance of debt	$ 562,000,000
Debt issuance costs											$ 500,000
Interest rate (as a percent)					2.50%		2.50%
Effective interest rate (as a percent)					12.07%	10.90%	12.07%	10.90%
Amount of debt prepaid			$ 10,000,000	$ 100,000,000	$ 57,500,000
Payment of a prepayment fee			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
Threshold limit to repay principal amount outstanding in full							$ 100,000,000
Threshold limit of asset dispositions which is required to make mandatory prepayments on senior notes							10,000,000
Maturity of debt
2018 (remainder)					25,000,000		25,000,000
2019					120,000,000		120,000,000
2020					80,000,000		80,000,000
2021					82,500,000		82,500,000
Total					307,500,000		307,500,000			365,000,000
Carrying amounts of the liability component
Principal amount of the Notes					307,500,000		307,500,000			365,000,000
Unamortized debt discount balance					(3,589,000)		(3,589,000)			(4,717,000)
Unamortized debt issuance costs					(2,330,000)		(2,330,000)			(3,063,000)
Net carrying amount of the Senior Notes					301,581,000		301,581,000			357,220,000
Interest expense incurred
Contractual/Stated coupon interest					9,425,000	$ 10,393,000	19,866,000	$ 23,159,000
Amortization of debt discount and debt issuance costs					853,000	595,000	1,861,000	1,197,000
Total interest expense					10,278,000	10,988,000	$ 21,727,000	24,356,000
Amendment fee			$ 3,000,000
Senior Notes | After Fifth Anniversary
Debt
Prepayment premium							0.00%
Senior Notes | After Second Anniversary and on or Prior to Third Anniversary
Debt
Prepayment premium							4.00%
Senior Notes | October 1, 2017 to September 30, 2018 | Minimum
Debt
Twelve month EBITDA required per the covenants							$ 90,000,000
Senior Notes | After September 30, 2018 | Minimum
Debt
Twelve month EBITDA required per the covenants							125,000,000
Senior Notes | Forecast
Maturity of debt
Principal payments									$ 105,000,000
Senior Notes | Three month LIBOR
Debt
Basis spread (as a percent)	9.75%
Interest rate through third anniversary (as a percent)	11.95%
Interest rate after third anniversary (as a percent)	12.95%
Senior Notes | Three month LIBOR | Minimum
Debt
Interest rate (as a percent)	1.00%
Senior Notes | NUCYNTA
Debt
Proceeds from the issuance of debt	$ 550,000,000
Convertible debt
Debt
Aggregate principal amount of notes issued		$ 345,000,000			$ 345,000,000		$ 345,000,000			$ 345,000,000
Interest rate (as a percent)		2.50%			2.50%		2.50%			2.50%
Effective interest rate (as a percent)		9.34%
Maturity of debt
Total					$ 345,000,000		$ 345,000,000			$ 345,000,000
Carrying amounts of the liability component
Principal amount of the Notes					345,000,000		345,000,000			345,000,000
Unamortized debt discount balance					(63,357,000)		(63,357,000)			(71,799,000)
Unamortized debt issuance costs					(3,186,000)		(3,186,000)			(3,691,000)
Net carrying amount of the Senior Notes					278,457,000		278,457,000			$ 269,510,000
Interest expense incurred
Contractual/Stated coupon interest					2,156,000	2,156,000	4,312,000	4,312,000
Amortization of debt discount and debt issuance costs					4,537,000	4,165,000	8,947,000	8,213,000
Total interest expense					$ 6,693,000	$ 6,321,000	$ 13,259,000	$ 12,525,000
Net proceeds from debt offering		$ 334,200,000
Underwriting discount		10,400,000
Offering expenses		$ 400,000
Trading days, number | item		20
Consecutive trading days, period | item		30
Stock price trigger | $ / shares		$ 25.01
Stock price trigger (as a percent)		130.00%
Conversion price (in dollars per share) | $ / shares		$ 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 (as a percent)		98.00%
Conversion rate of common stock per $1 of principal amount		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
Interest expense incurred
Equity issuance costs		$ 3,700,000