Summary of Other Current Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Prepaid Expense And Other Assets Current [Abstract]
Manufacturing-related deposits and prepaids	$ 123,895	$ 54,276
Prepaid clinical and pre-clinical expenses	14,109	8,263
Prepaid insurance	5,532	2,573
Prepaid research expenses	5,392	2,007
Prepaid income tax	5,270	2,114
Prepaid maintenance services	4,136	4,366
Leasehold improvement receivable	3,059	3,059
Other	3,231	5,249
Total other current assets	$ 164,624	$ 81,907