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Cash and Investments - Narrative (Details)
3 Months Ended
Mar. 30, 2018
USD ($)
investment
Mar. 31, 2017
USD ($)
Dec. 29, 2017
investment
Investments, Debt and Equity Securities [Abstract]      
Number of investments in an unrealized loss position | investment 150   134
Other-than-temporary impairment charges on available-for-sale securities | $ $ 0 $ 0