Accrued expenses and other current liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Employee compensation	$ 16,404	$ 28,567
Accrued manufacturing costs	12,125	21,618
Accrued clinical and contract research organization costs	14,724	11,891
Accrued license and milestone fees	323	7,739
Accrued professional fees	1,906	1,830
Financing lease obligation, current portion		1,424
Other	30,670	26,324
Total accrued expenses and other current liabilities	$ 76,152	$ 99,393