Business Combinations and Contingent Consideration - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions				1 Months Ended			3 Months Ended	9 Months Ended
	Mar. 10, 2016	Jul. 17, 2013	Sep. 05, 2012	Apr. 30, 2016	Mar. 31, 2016	Mar. 31, 2013	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Business Acquisition [Line Items]
License fees received						$ 3,000,000
Historical Cost								$ 305,668,000		$ 305,668,000
Acquisition related contingent obligations								0	$ (1,300,000)
In-process research and development [Member]
Business Acquisition [Line Items]
Estimated cash flow period						10 years
Estimated cash flow discount rate						25.00%
Ligand Pharmaceuticals Inc [Member]
Business Acquisition [Line Items]
Milestone payments	$ 6,000,000			$ 6,000,000	$ 6,000,000
Melphalan In Process Research and Development [Member]
Business Acquisition [Line Items]
Historical Cost				$ 7,700,000				$ 7,700,000		$ 7,700,000
Minimum [Member]
Business Acquisition [Line Items]
Royalties payout percentage on our future net sales of licensed products								20.00%
Milestone Payments [Member]
Business Acquisition [Line Items]
Milestone payments		$ 5,000,000.0						$ 60,000,000
Milestone net sales achievement		30,000,000.0
Ligand Contingent Consideration					6,000,000		$ 6,000,000
Milestone Payment One [Member]
Business Acquisition [Line Items]
Milestone payments		10,000,000.0
Milestone net sales achievement		60,000,000.0
Milestone Payment Two [Member]
Business Acquisition [Line Items]
Milestone payments		25,000,000.0
Milestone net sales achievement		100,000,000.0
Milestone Payment Three [Member]
Business Acquisition [Line Items]
Milestone payments		50,000,000.0
Milestone net sales achievement		200,000,000.0
Milestone Payment Four [Member]
Business Acquisition [Line Items]
Milestone payments		100,000,000.0
Milestone net sales achievement		400,000,000.0
Menadione Topical Lotion [Member]
Business Acquisition [Line Items]
Milestone payments		5,000,000.0
Talon Therapeutics, Inc. [Member]
Business Acquisition [Line Items]
Additional shares business acquisition date								Jul. 17, 2013
Cash consideration		$ 11,300,000
Shares issued in acquisition (shares)		3.0
Common stock value assigned		$ 26,300,000
Common stock value, per share ($ per share)		$ 8.77
Estimated fair value of acquisition		$ 6,500,000
Contingent value rights future cash payments		$ 195,000,000.0						$ 195,000,000
Talon Therapeutics, Inc. [Member] | Minimum [Member]
Business Acquisition [Line Items]
Contingent value rights expected rate		50.00%
Talon Therapeutics, Inc. [Member] | Maximum [Member]
Business Acquisition [Line Items]
Contingent value rights expected rate		100.00%
Ligand Pharmaceuticals Inc [Member]
Business Acquisition [Line Items]
Ligand Contingent Consideration					$ 6,000,000		6,000,000
Acquisition related contingent obligations							$ 800,000
Allos Therapeutics, Inc. [Member]
Business Acquisition [Line Items]
Cash consideration			$ 205,200,000