Condensed Consolidated Balance Sheet Components - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accrued Liabilities Current [Abstract]
Accrued personnel expenses	$ 2,761	$ 1,026
Accrued research and development expenses	3,604	1,193
Professional fees	116	706
Other	186	212
Total	$ 6,667	$ 3,137	[1]

[1] The Condensed Consolidated Balance Sheet as of December 31, 2017 has been derived from the audited financial statements as of that date.