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Cash and Investments - Narrative (Details) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 28, 2018 USD ($) investment | Sep. 29, 2017 USD ($) | Sep. 29, 2018 USD ($) | Sep. 28, 2018 USD ($) investment | Sep. 29, 2017 USD ($) | Dec. 29, 2017 USD ($) investment
Investments, Debt and Equity Securities [Abstract] |  |  |  |  |  |
Gain (loss) on sales of investments available-for-sale | $ 0 | $ 0 |  | $ 0 | $ 0 |
Number of investments in an unrealized loss position | investment | 151 |  |  | 151 |  | 134
Other-than-temporary impairment charges on available-for-sale securities | $ 0 | $ 0 |  | $ 0 | $ 0 |
Beneficial ownership interest by BlackRock (more than) | 10.00% |  |  | 10.00% |  |
Fair value of cash and investments managed by BlackRock | $ 263,500,000 |  |  | $ 263,500,000 |  | $ 141,000,000
Fair value of cash and investments managed by BlackRock in the BlackRock Liquidity Money Market Fund | $ 21,300,000 |  |  | $ 21,300,000 |  | $ 1,100,000
Fees for advisory services paid to BlackRock |  |  | $ 100,000 |  |  |

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