Accounts Payable and Other Liabilities - Schedule of Accounts Payable and Other Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Trade accounts payable	$ 6,016	$ 6,860
Accrued clinical/preclinical expenses	2,667	1,381
Accrued compensation and vacation	1,553	1,024
Other liabilities	720	254
Accounts payable and other liabilities	$ 10,956	$ 9,519