Accrued Liabilities - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accrued payroll and related expenses	$ 789	$ 394
Accrued research and development expenses	2,214	3,250
Deferred offering costs		238
Other	360	105
Total accrued liabilities	$ 3,363	$ 3,987