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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

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