Prepaid Expenses and Other Current Assets - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Prepaid Expense and Other Assets, Current [Abstract]
Tax incentive refund	$ 1,325
Prepaid research and development costs	981	$ 163
Prepaid insurance	316
Interest income receivable	220
Prepaid rent	81	122
Other current assets	795	60
Total	$ 3,718	$ 345