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Fair Value Measurements (Schedule of Fair Value of Financial Assets Measured on A Recurring Basis) (Details) - USD ($)
$ in Thousands
Dec. 29, 2017
Dec. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total financial assets $ 440,410 $ 459,966
Money market funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total financial assets 45,478 71,457
Commercial paper [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total financial assets 199,647 165,375
Corporate bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total financial assets 179,022 152,407
US Treasury and Government [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total financial assets 16,263 70,727
Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total financial assets 45,478 71,457
Level 1 [Member] | Money market funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total financial assets 45,478 71,457
Level 1 [Member] | Commercial paper [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total financial assets 0 0
Level 1 [Member] | Corporate bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total financial assets 0 0
Level 1 [Member] | US Treasury and Government [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total financial assets 0 0
Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total financial assets 394,932 388,509
Level 2 [Member] | Money market funds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total financial assets 0 0
Level 2 [Member] | Commercial paper [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total financial assets 199,647 165,375
Level 2 [Member] | Corporate bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total financial assets 179,022 152,407
Level 2 [Member] | US Treasury and Government [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total financial assets $ 16,263 $ 70,727