Temporarily Impaired Available for Sale Securities by Time Period Impaired (Detail) - USD ($) $ in Thousands	Dec. 29, 2018	Dec. 30, 2017
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 699,216	$ 2,355,037
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	6,262	18,735
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,646,991	1,289,862
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	61,928	23,128
Debt Securities, Available-for-sale, Unrealized Loss Position	3,346,207	3,644,899
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	68,190	41,863
Tax exempt bonds
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	25,150	1,543,151
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	95	13,827
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,182,783	136,217
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	12,664	2,593
Debt Securities, Available-for-sale, Unrealized Loss Position	1,207,933	1,679,368
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	12,759	16,420
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	645,379	811,886
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5,821	4,908
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,464,208	1,153,645
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	49,264	20,535
Debt Securities, Available-for-sale, Unrealized Loss Position	2,109,587	1,965,531
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	55,085	25,443
Debt Securities, Restricted [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	28,687	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	346	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position	28,687	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 346	$ 0