Accrued Expenses - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Liabilities, Current [Abstract]
Compensation and benefit costs	$ 2,616	$ 794
Research and development costs	3,969	831
Consulting and professional fees	320	267
Preferred stock issuance cost		85
Other liabilities	917	121
Accrued expenses	$ 7,822	$ 2,098