Accrued and Other Liabilities - Schedule of Accrued Liabilities and Other Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Accrued clinical and non-clinical expenses	$ 5,447	$ 6,694
Accrued contract manufacturing	3,980	2,705
Accrued professional and consulting services	530	322
Other	752	684
Accrued liabilities and other liabilities	$ 10,709	$ 10,405