Fair Value Measurements - Fair Value Measurement Activity for Liabilities Utilize Level 3 Inputs (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 21,352	$ 23,127
Ending Balance	22,218	21,352
Deferred development costs [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers in (out) of Level 3	(176)	(1,099)
Ligand Contingent Consideration [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers in (out) of Level 3	773	326
Talon CVR [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers in (out) of Level 3	269	(1,002)
Corixa Liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers in (out) of Level 3	$ 0	$ 0