Balance Sheet Account Detail - Components of Intangible Assets Net of Accumulated Amortization (Detail) - USD ($) $ in Thousands			1 Months Ended	3 Months Ended		12 Months Ended
	Mar. 10, 2016	May. 29, 2013	Mar. 31, 2016	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Product Rights [Line Items]
Historical Cost			$ 305,668	$ 305,668		$ 305,668
Accumulated Amortization			(109,166)	(109,166)		(102,797)
Foreign Currency Translation				(3,566)		(4,353)
Impairment				(8,183)		(8,183)
Net Amount			184,753	184,753		190,335
Ligand Pharmaceuticals Inc [Member]
Product Rights [Line Items]
Milestone payments	$ 6,000		6,000
MARQIBO IPR&D (NHL indication) [Member]
Product Rights [Line Items]
Historical Cost			17,600	17,600		17,600
Accumulated Amortization			0	0		0
Foreign Currency Translation				0		0
Impairment				0		0
Net Amount			17,600	17,600		17,600
EVOMELA distribution rights [Member]
Product Rights [Line Items]
Historical Cost			7,700	7,700		7,700
Accumulated Amortization			0	0		0
Foreign Currency Translation				0		0
Impairment				0		0
Net Amount			7,700	$ 7,700		7,700
Full Amortization Period (months)				156 months
Remaining Amortization Period (months)				156 months
BELEODAQ distribution rights [Member]
Product Rights [Line Items]
Historical Cost			25,000	$ 25,000		25,000
Accumulated Amortization			(3,281)	(3,281)		(2,812)
Foreign Currency Translation				0		0
Impairment				0		0
Net Amount			21,719	$ 21,719		22,188
Full Amortization Period (months)				160 months
Remaining Amortization Period (months)				139 months
MARQIBO distribution rights [Member]
Product Rights [Line Items]
Historical Cost			26,900	$ 26,900		26,900
Accumulated Amortization			(9,624)	(9,624)		(8,544)
Foreign Currency Translation				0		0
Impairment				0		0
Net Amount			17,276	$ 17,276		18,356
Full Amortization Period (months)				81 months
Remaining Amortization Period (months)				48 months
FOLOTYN distribution rights [Member]
Product Rights [Line Items]
Historical Cost			118,400	$ 118,400		118,400
Accumulated Amortization			(31,834)	(31,834)		(29,474)
Foreign Currency Translation				0		0
Impairment		$ (1,000)		0		0
Net Amount			86,566	$ 86,566		88,926
Full Amortization Period (months)				152 months
Remaining Amortization Period (months)				110 months
ZEVALIN distribution rights [Member] | United States [Member]
Product Rights [Line Items]
Historical Cost			41,900	$ 41,900		41,900
Accumulated Amortization			(31,477)	(31,477)		(30,608)
Foreign Currency Translation				0		0
Impairment				0		0
Net Amount			10,423	$ 10,423		11,292
Full Amortization Period (months)				123 months
Remaining Amortization Period (months)				36 months
ZEVALIN distribution rights [Member] | Ex-U.S. [Member]
Product Rights [Line Items]
Historical Cost			23,490	$ 23,490		23,490
Accumulated Amortization			(13,543)	(13,543)		(12,632)
Foreign Currency Translation				(3,566)		(4,353)
Impairment				0		0
Net Amount			6,381	$ 6,381		6,505
Full Amortization Period (months)				96 months
Remaining Amortization Period (months)				48 months
FUSILEV distribution rights [Member]
Product Rights [Line Items]
Historical Cost			16,778	$ 16,778		16,778
Accumulated Amortization			(9,618)	(9,618)		(9,618)
Foreign Currency Translation				0		0
Impairment				(7,160)		(7,160)
Net Amount			0	$ 0		0
Full Amortization Period (months)				56 months
Remaining Amortization Period (months)				0 months
FOLOTYN out-License [Member]
Product Rights [Line Items]
Historical Cost			27,900	$ 27,900		27,900
Accumulated Amortization			(9,789)	(9,789)		(9,109)
Foreign Currency Translation				0		0
Impairment				(1,023)		(1,023)
Net Amount			17,088	$ 17,088		$ 17,768
Full Amortization Period (months)				110 months
Remaining Amortization Period (months)				76 months
FUSILEV [Member]
Product Rights [Line Items]
Impairment					$ (7,200)
EVOMELA [Member]
Product Rights [Line Items]
Historical Cost			$ 7,700	$ 7,700