Summary of Other Current Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Prepaid Expense And Other Assets Current [Abstract]
Manufacturing-related deposits and prepaids	$ 55,322	$ 39,036
Investment receivable	42,300
Leasehold improvement receivable	13,474	13,474
Prepaid clinical and pre-clinical expenses	10,149	9,706
Prepaid maintenance services	3,538	2,994
Prepaid research expenses	3,091	1,932
Prepaid income tax	2,130	2,130
Interest receivable	1,285	1,918
Other	4,949	6,592
Total other current assets	$ 136,238	$ 77,782