Accrued Expense - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts Payable and Accrued Liabilities [Line Items]
Accrued expense	$ 739	$ 969
Accrued Vacation And Bonus	100	400
Accrued Laboratory Expense		200
Accrued Clinical And Preclinical	400	200
Accrued License Maintenance Fee	100	100
Other Accrued Liabilities	$ 100	$ 100