Condensed Consolidated Balance Sheet Components - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accrued Liabilities Current [Abstract]
Accrued personnel expenses	$ 3,455	$ 2,833
Accrued research and development expenses	5,805	2,816
Professional fees	281	211
Other	121	163
Total	$ 9,662	$ 6,023	[1]

[1] The Condensed Consolidated Balance Sheet as of December 31, 2018 has been derived from the audited financial statements as of that date.