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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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Minority Ownership, Ownership Interest

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Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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Amount of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in earnings and other comprehensive loss (OCI).

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