Accounts Payable, Accrued Expenses and Other - Schedule of Accounts Payable, Accrued Expenses and Other (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accounts payable	$ 1,750	$ 2,887
Accrued goods and services	2,810	5,682
Accrued clinical trial costs	3,978	3,901
Accrued drug purchase costs	4,140	222
Accrued payroll and related benefits	1,489	2,884
Accrued restructuring expenses		628
Deferred tax incentives	1,402	1,402
Total accounts payable, accrued expenses and other	$ 15,569	$ 17,606