Accounts Payable and Accrued Expenses - Schedule of Accounts Payable and Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accounts payable	$ 4,371	$ 3,829
Accrued research projects	6,079	2,356
Accrued professional fees	802	384
Accrued compensation and benefits	2,370	1,864
Accrued other		73
Total	$ 13,622	$ 8,506