Condensed Consolidated Balance Sheet Components - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accrued Liabilities Current [Abstract]
Accrued personnel expenses	$ 1,963	$ 2,833
Accrued research and development expenses	4,954	2,816
Professional fees	519	211
Other	193	163
Total	$ 7,629	$ 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.