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Balance Sheet Components (Schedule of Available-for-Sale Short-Term Investments) (Details) - U.S. treasuries - USD ($)
$ in Thousands
9 Months Ended 12 Months Ended
Sep. 29, 2019
Dec. 31, 2018
Debt Securities, Available-For-Sale [Line Items]    
Cost $ 39,897 $ 49,739
Unrealized Gains 44 2
Unrealized Losses 0 (4)
Estimated Fair Value $ 39,941 $ 49,737