Fair Value Measurements - Fair Value Measurement Activity for Liabilities Utilize Level 3 Inputs (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning	$ 14,445	$ 21,352
Settlement of Ligand Contingent Consideration liability - EVOMELA (see Note 9(b))		(6,000)
Ending	16,977	14,445
FOLOTYN development liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Increase/decrease	(704)	(1,556)
Ligand Contingent Consideration [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Increase/decrease		773
Talon CVR [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Increase/decrease	$ 3,236	$ (124)