Temporarily Impaired Available for Sale Debt Securities by Time Period Impaired (Details) - USD ($) $ in Thousands	Mar. 27, 2021	Dec. 26, 2020
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 2,972,967	$ 1,161,091
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	58,870	8,034
Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	39,629	39,622
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	371	378
Unrealized Loss Position, Fair Value	3,012,596	1,200,713
Unrealized Loss Position, Accumulated Loss	59,241	8,412
Tax exempt bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	9,961	3,704
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	47	88
Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	0	0
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Unrealized Loss Position, Fair Value	9,961	3,704
Unrealized Loss Position, Accumulated Loss	47	88
Taxable bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	2,963,006	1,157,387
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	58,823	7,946
Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	39,629	39,622
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	371	378
Unrealized Loss Position, Fair Value	3,002,635	1,197,009
Unrealized Loss Position, Accumulated Loss	$ 59,194	$ 8,324