Temporarily Impaired Available for Sale Securities by Time Period Impaired (Detail) - USD ($) $ in Thousands	Mar. 30, 2019	Dec. 29, 2018
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 48,343	$ 699,216
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	329	6,262
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,465,473	2,646,991
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	25,829	61,928
Debt Securities, Available-for-sale, Unrealized Loss Position	2,513,816	3,346,207
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	26,158	68,190
Nontaxable Municipal Bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	2,812	25,150
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	19	95
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,100,840	1,182,783
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	5,208	12,664
Debt Securities, Available-for-sale, Unrealized Loss Position	1,103,652	1,207,933
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	5,227	12,759
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	45,531	645,379
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	310	5,821
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,364,633	1,464,208
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	20,621	49,264
Debt Securities, Available-for-sale, Unrealized Loss Position	1,410,164	2,109,587
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	20,931	55,085
Debt Securities, Restricted [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	0	28,687
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	346
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	0	28,687
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 0	$ 346