Temporarily Impaired Available for Sale Securities by Time Period Impaired (Detail) - USD ($) $ in Thousands	Mar. 26, 2016	Dec. 26, 2015
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	$ 1,785,939	$ 3,005,302
Less Than 12 Months, Unrealized Losses	31,283	34,202
12 Months or Longer, Fair Value	210,529	149,895
12 Months or Longer, Unrealized Losses	8,260	6,680
Total, Fair Value	1,996,468	3,155,197
Total, Unrealized Losses	39,543	40,882
Tax exempt bonds
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	533,673	890,907
Less Than 12 Months, Unrealized Losses	2,736	2,264
12 Months or Longer, Fair Value	11,743	63,474
12 Months or Longer, Unrealized Losses	45	473
Total, Fair Value	545,416	954,381
Total, Unrealized Losses	2,781	2,737
Taxable bonds
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	730,768	1,676,719
Less Than 12 Months, Unrealized Losses	2,950	9,988
12 Months or Longer, Fair Value	176,955	70,309
12 Months or Longer, Unrealized Losses	599	411
Total, Fair Value	907,723	1,747,028
Total, Unrealized Losses	3,549	10,399
Restricted investments
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	164,240	163,159
Less Than 12 Months, Unrealized Losses	309	1,389
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Total, Fair Value	164,240	163,159
Total, Unrealized Losses	309	1,389
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	357,258	274,517
Less Than 12 Months, Unrealized Losses	25,288	20,561
12 Months or Longer, Fair Value	21,831	16,112
12 Months or Longer, Unrealized Losses	7,616	5,796
Total, Fair Value	379,089	290,629
Total, Unrealized Losses	$ 32,904	$ 26,357