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Investments (Narrative) (Details) | 12 Months Ended |
--- | --- | ---
Dec. 29, 2017 USD ($) investment | Dec. 30, 2016 USD ($) investment | Jan. 01, 2016 USD ($) | Aug. 31, 2016
Investment [Line Items] |  |  |  |
Gain (loss) on sale of available-for-sale securities | $ 0 | $ 0 | $ 0 |
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | investment | 134 | 86 |  |
Other-than-temporary impairment charges on available-for-sale securities | $ 0 | $ 0 | 0 |
Akarna Therapeutics, Ltd. [Member] |  |  |  |
Investment [Line Items] |  |  |  |
Realized gain on sale of cost method investment | $ 3,000,000 | 2,500,000 | $ 0 |
Cost method investment ownership percentage |  |  |  | 9.00%
Silicon Valley Bank Term Loan and Line of Credit [Member] |  |  |  |
Investment [Line Items] |  |  |  |
Collateral balance |  | $ 81,600,000 |  |

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