Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Accrued contract manufacturing costs	$ 13,438	$ 4,673
Accrued clinical and preclinical costs	13,123	10,033
Accrued employee compensation costs	10,560	8,748
Accrued professional fees	5,520	2,799
Product revenue related reserves	4,095	305
Accrued income taxes	3,493
Accrued BioMarin royalties	2,289
Accrued research costs	317	1,186
Other	2,917	3,272
Total accrued expenses	$ 55,752	$ 31,016