Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued legal and professional expenses	$ 4,837	$ 1,633
Accrued employee compensation and benefits	3,803	6,175
Accrued research and development	2,485	2,328
Accrued other	773	606
Total accrued expenses	$ 11,898	$ 10,742