Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Development and manufacturing costs	$ 7,389	$ 3,910
Payroll and payroll-related costs	3,982	4,962
Professional fees	462	344
Facility and other	2,801	3,297
Total Accrued Expenses and Other Current Liabilities	$ 14,634	$ 12,513