Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Payables And Accruals [Abstract]
Accrued clinical and preclinical costs	$ 9,094	$ 9,587
Accrued employee compensation costs	7,649	8,189
Accrued contract manufacturing costs	7,605	4,830
Accrued professional fees	2,280	4,258
Accrued research costs	1,746	629
Other	1,165	1,560
Total accrued expenses	$ 29,539	$ 29,053