Balance Sheet Components - Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued compensation	$ 8,739	$ 9,952
Accrued clinical costs	5,042	2,091
Accrued manufacturing and other research & development costs	5,251	4,179
Accrued general, administrative and shared costs	1,310	2,250
Deferred rent, current		616
Operating lease liability, current	3,665
Other current liabilities	8	380
Total accrued expenses and other current liabilities	$ 24,015	$ 19,468