Investments Available for Sale Securities Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 30, 2019	Dec. 29, 2018
Debt Securities, Available-for-sale [Line Items]
Cost	$ 4,341,101	$ 3,944,459
Debt Securities, Available-for-sale, Unrealized Gain	40,615	2,441
Debt Securities, Available-for-sale, Unrealized Loss	26,158	68,190
Debt Securities, Available-for-sale	4,355,558	3,878,710
Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	1,189,068	1,256,673
Debt Securities, Available-for-sale, Unrealized Gain	633	184
Debt Securities, Available-for-sale, Unrealized Loss	5,227	12,759
Debt Securities, Available-for-sale	1,184,474	1,244,098
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	2,982,504	2,527,468
Debt Securities, Available-for-sale, Unrealized Gain	34,563	1,737
Debt Securities, Available-for-sale, Unrealized Loss	20,931	55,085
Debt Securities, Available-for-sale	2,996,136	2,474,120
Debt Securities, Restricted [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	169,529	160,318
Debt Securities, Available-for-sale, Unrealized Gain	5,419	520
Debt Securities, Available-for-sale, Unrealized Loss	0	346
Debt Securities, Available-for-sale	$ 174,948	$ 160,492

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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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+ 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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