Summary of Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Prepaid Expense And Other Assets Current [Abstract]
Manufacturing-related deposits and prepaids	$ 18,650	$ 23,604
Prepaid clinical and preclinical expenses	5,175	1,225
Prepaid research expenses	2,896
Prepaid maintenance services	1,711	109
Prepaid commercial expenses	1,589	54
Asset held for sale	1,501
Other prepaids	2,726	989
Other	2,263	914
Total other current assets	$ 36,511	$ 26,895