Investments Available for Sale Debt Securities Reconciliation (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 26, 2020	Dec. 28, 2019
Debt Securities, Available-for-sale [Line Items]
Cost	$ 8,242,309	$ 5,939,950
Debt Securities, Available-for-sale, Unrealized Gain	301,504	133,662
Debt Securities, Available-for-sale, Unrealized Loss	8,034	1,573
Debt Securities, Available-for-sale	8,535,779	6,072,039
Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	596,669	767,931
Debt Securities, Available-for-sale, Unrealized Gain	9,110	3,429
Debt Securities, Available-for-sale, Unrealized Loss	136	130
Debt Securities, Available-for-sale	605,643	771,230
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	7,478,037	5,002,036
Debt Securities, Available-for-sale, Unrealized Gain	276,735	120,132
Debt Securities, Available-for-sale, Unrealized Loss	7,898	1,443
Debt Securities, Available-for-sale	7,746,874	5,120,725
Restricted Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost	167,603	169,983
Debt Securities, Available-for-sale, Unrealized Gain	15,659	10,101
Debt Securities, Available-for-sale, Unrealized Loss	0	0
Debt Securities, Available-for-sale	$ 183,262	$ 180,084

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

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