Temporarily Impaired Available for Sale Securities by Time Period Impaired (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 26, 2015
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	$ 4,507,220	$ 3,005,302
Less than 12 Months, Unrealized Loss	62,157	34,202
12 Months or Longer, Fair Value	96,009	149,895
12 Months or Longer, Unrealized Loss	4,814	6,680
Total, Fair Value	4,603,229	3,155,197
Total, Unrealized Loss	66,971	40,882
Tax exempt bonds
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	2,360,143	890,907
Less than 12 Months, Unrealized Loss	24,416	2,264
12 Months or Longer, Fair Value	6,099	63,474
12 Months or Longer, Unrealized Loss	233	473
Total, Fair Value	2,366,242	954,381
Total, Unrealized Loss	24,649	2,737
Taxable bonds
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	1,921,367	1,676,719
Less than 12 Months, Unrealized Loss	33,354	9,988
12 Months or Longer, Fair Value	51,769	70,309
12 Months or Longer, Unrealized Loss	549	411
Total, Fair Value	1,973,136	1,747,028
Total, Unrealized Loss	33,903	10,399
Restricted investments
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	164,085	163,159
Less than 12 Months, Unrealized Loss	463	1,389
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Loss	0	0
Total, Fair Value	164,085	163,159
Total, Unrealized Loss	463	1,389
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	61,625	274,517
Less than 12 Months, Unrealized Loss	3,924	20,561
12 Months or Longer, Fair Value	38,141	16,112
12 Months or Longer, Unrealized Loss	4,032	5,796
Total, Fair Value	99,766	290,629
Total, Unrealized Loss	$ 7,956	$ 26,357