Investments Available for Sale Securities Reconciliation (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 29, 2018	Dec. 30, 2017
Debt Securities, Available-for-sale [Line Items]
Cost	$ 3,747,239	$ 3,926,697
Debt Securities, Available-for-sale, Unrealized Gain	450	1,297
Debt Securities, Available-for-sale, Unrealized Loss	79,086	41,863
Debt Securities, Available-for-sale	3,668,603	3,886,131
Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	1,340,795	1,811,523
Debt Securities, Available-for-sale, Unrealized Gain	110	602
Debt Securities, Available-for-sale, Unrealized Loss	20,347	16,420
Debt Securities, Available-for-sale	1,320,558	1,795,705
Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	2,406,444	2,115,174
Debt Securities, Available-for-sale, Unrealized Gain	340	695
Debt Securities, Available-for-sale, Unrealized Loss	58,739	25,443
Debt Securities, Available-for-sale	$ 2,348,045	$ 2,090,426

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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-SubTopic 10
-Section 50
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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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Amount of 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/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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