Accounts Payable and Accrued Expenses - Schedule of Accounts Payable and Accrued Expenses (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Accounts payable	$ 1,865	$ 4,738
Accrued research projects	3,531	4,352
Accrued professional fees	323	163
Accrued compensation and benefits	1,119	1,514
Accrued other	352	766
Total	$ 7,190	$ 11,533