Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Product revenue related reserves	$ 26,146	$ 7,302
Accrued employee compensation costs	24,692	14,402
Accrued milestone expense	24,020
Accrued contract manufacturing costs	15,794	14,019
Accrued clinical and pre-clinical costs	11,396	15,975
Accrued professional fees	11,319	6,794
Accrued BioMarin royalties	8,254	2,846
Accrued property and equipment	5,421	2,525
Accrued collaboration cost sharing	2,167
Accrued research costs	1,070	401
Accrued interest expenses	1,045	1,291
Accrued income taxes	301	943
Other	2,470	2,484
Total accrued expenses	$ 134,095	$ 68,982