Accrued Expense - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts Payable and Accrued Liabilities [Line Items]
Accrued expense	$ 456	$ 304
Accrued Vacation And Bonus	200	100
Accrued Clinical And Preclinical Expenses	100	100
Other Accrued Liabilities	100
Accrued Legal And Professional Fee	$ 100	$ 100