Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Development and clinical manufacturing costs	$ 3,910	$ 3,350
Payroll and payroll-related costs	4,962	3,698
Professional fees	344	448
Facility and other	3,297	3,316
Total Accrued Expenses and Other Current Liabilities	$ 12,513	$ 10,812