Inventory - Summary of Inventories (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw materials	$ 1,493		$ 1,493		$ 469
Work in process	43,761		43,761		25,160
Finished goods	3,330		3,330		3,066
Total inventory	48,584		48,584		$ 28,695
Inventory written off	$ 1,200	$ 300	$ 5,288	$ 335