Temporarily Impaired Available for Sale Securities by Time Period Impaired (Detail) - USD ($) $ in Thousands	Jun. 25, 2016	Dec. 26, 2015
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	$ 588,930	$ 3,005,302
Less Than 12 Months, Unrealized Losses	19,329	34,202
12 Months or Longer, Fair Value	177,887	149,895
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	11,576	6,680
Total, Fair Value	766,817	3,155,197
Total, Unrealized Losses	30,905	40,882
Tax exempt bonds
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	90,715	890,907
Less Than 12 Months, Unrealized Losses	532	2,264
12 Months or Longer, Fair Value	11,641	63,474
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	27	473
Total, Fair Value	102,356	954,381
Total, Unrealized Losses	559	2,737
Taxable bonds
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	140,993	1,676,719
Less Than 12 Months, Unrealized Losses	153	9,988
12 Months or Longer, Fair Value	132,257	70,309
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	988	411
Total, Fair Value	273,250	1,747,028
Total, Unrealized Losses	1,141	10,399
Restricted investments
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	0	163,159
Less Than 12 Months, Unrealized Losses	0	1,389
12 Months or Longer, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Total, Fair Value	0	163,159
Total, Unrealized Losses	0	1,389
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	357,222	274,517
Less Than 12 Months, Unrealized Losses	18,644	20,561
12 Months or Longer, Fair Value	33,989	16,112
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	10,561	5,796
Total, Fair Value	391,211	290,629
Total, Unrealized Losses	$ 29,205	$ 26,357