Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Product revenue related reserves	$ 12,712	$ 7,302
Accrued clinical and preclinical costs	10,924	15,975
Accrued professional fees	10,351	6,794
Accrued employee compensation costs	7,906	14,402
Accrued contract manufacturing costs	7,025	14,019
Accrued interest expense	3,411	1,291
Accrued collaboration cost sharing	3,197
Accrued BioMarin royalties	3,117	2,846
Accrued property and equipment	2,980	2,525
Accrued income taxes	943	943
Accrued research costs	226	401
Other	2,856	2,484
Total accrued expenses	$ 65,648	$ 68,982