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Balance Sheet Components (Allowance for Doubtful Accounts) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Allowance for Doubtful Accounts [Roll Forward]    
Balance at beginning of year $ 23 $ 21
Additions charged 18 2
Balance at end of year $ 41 $ 23