Temporarily Impaired Available for Sale Debt Securities by Time Period Impaired (Details) - USD ($) $ in Thousands	Dec. 28, 2019	Dec. 29, 2018
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months	$ 621,777	$ 699,216
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	899	6,262
Continuous Unrealized Loss Position, 12 Months or Longer	297,617	2,646,991
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	674	61,928
Debt Securities, Unrealized Loss Position	919,394	3,346,207
Debt Securities, Unrealized Loss Position, Accumulated Loss	1,573	68,190
Tax exempt bonds
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months	48,462	25,150
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	11	95
Continuous Unrealized Loss Position, 12 Months or Longer	99,976	1,182,783
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	119	12,664
Debt Securities, Unrealized Loss Position	148,438	1,207,933
Debt Securities, Unrealized Loss Position, Accumulated Loss	130	12,759
Taxable Bonds
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months	573,315	645,379
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	888	5,821
Continuous Unrealized Loss Position, 12 Months or Longer	197,641	1,464,208
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	555	49,264
Debt Securities, Unrealized Loss Position	770,956	2,109,587
Debt Securities, Unrealized Loss Position, Accumulated Loss	1,443	55,085
Restricted Investments
Debt Securities, Available-for-sale [Line Items]
Continuous Unrealized Loss Position, Less than 12 Months	0	28,687
Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	346
Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Unrealized Loss Position	0	28,687
Debt Securities, Unrealized Loss Position, Accumulated Loss	$ 0	$ 346