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Balance Sheet Components (Schedule of Available-for-Sale Short-Term Investments) (Details) - USD ($)
$ in Thousands
Jul. 01, 2018
Dec. 31, 2017
Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Cost $ 125,894 $ 124,978
Unrealized Gains 0 0
Unrealized Losses (115) (146)
Estimated Fair Value 125,779 124,832
U.S. treasuries    
Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Cost 125,740 124,816
Unrealized Gains 0 0
Unrealized Losses (115) (146)
Estimated Fair Value 125,625 124,670
Certificates of deposit    
Available-for-sale Securities, Amortized Cost Basis [Abstract]    
Cost 154 162
Unrealized Gains 0 0
Unrealized Losses 0 0
Estimated Fair Value $ 154 $ 162