Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued employee compensation and benefits	$ 5,300	$ 6,175
Accrued research and development	2,911	2,328
Accrued legal and professional expenses	2,663	1,633
Accrued other	770	606
Total accrued expenses	$ 11,644	$ 10,742