Accounts Payable, Accrued Expenses and Other - Schedule of Accounts Payable, Accrued Expenses and Other (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accounts payable	$ 841	$ 1,034
Accrued goods and services	2,421	2,082
Accrued clinical trial costs	1,919	1,683
Accrued drug purchase costs	1,114	4,245
Accrued payroll and related benefits	833	2,315
Accrued restructuring expenses	209	921	$ 251	$ 628
Income taxes payable	83	83
Deferred tax incentives	1,314	1,314
Lease liability	1,605
Total accounts payable, accrued expenses and other	$ 10,339	$ 13,677