Balance Sheet Components - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accrued liabilities
Accrued payroll-related expenses	$ 1,236	$ 1,558
Accrued joint development agreement expenses	170	661
Accrued inventory	87	1,678
Restructuring expenses	782
Deferred rent		390
Other	452	714
Total accrued liabilities	$ 2,727	$ 5,001