Summary of Other Current Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Prepaid Expense And Other Assets Current [Abstract]
Manufacturing-related deposits and prepaids	$ 21,035	$ 23,604
Prepaid clinical and preclinical expenses	3,974	1,225
Other prepaids	2,416	1,152
Other	1,140	914
Total other current assets	$ 28,565	$ 26,895