Accrued Liabilities - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accrued bonus and payroll expenses	$ 3,190	$ 3,016
Accrued professional and consulting services	282	367
Accrued clinical and manufacturing expenses	5,960	4,845
Accrued preclinical and research expenses	458	469
Other	198	241
Total accrued liabilities	$ 10,088	$ 8,938