Balance Sheet Components - Accrued liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Balance Sheet Components
Accrued vacation	$ 319	$ 263
Customer advances	218	451
Accrued audit fees	139	140
Accrued compensation	157	38
Accrued rebate	33	204
Accrued other	73	50
Total accrued liabilities	$ 939	$ 1,146	[1]

[1] The condensed consolidated balance sheet as of December 31, 2019 was derived from the audited consolidated balance sheet as of that date.