Temporarily Impaired Available for Sale Securities by Time Period Impaired (Detail) - USD ($) $ in Thousands	Sep. 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	$ 1,989,943	$ 2,355,037
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	28,713	18,735
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,554,892	1,289,862
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	50,373	23,128
Debt Securities, Available-for-sale, Unrealized Loss Position	3,544,835	3,644,899
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	79,086	41,863
Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	775,195	1,543,151
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	8,384	13,827
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	537,591	136,217
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	11,963	2,593
Debt Securities, Available-for-sale, Unrealized Loss Position	1,312,786	1,679,368
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	20,347	16,420
Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	1,214,748	811,886
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	20,329	4,908
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,017,301	1,153,645
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	38,410	20,535
Debt Securities, Available-for-sale, Unrealized Loss Position	2,232,049	1,965,531
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 58,739	$ 25,443