Temporarily Impaired Available for Sale Securities by Time Period Impaired (Detail) - USD ($) $ in Thousands	Sep. 24, 2016	Dec. 26, 2015
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	$ 1,809,383	$ 3,005,302
Less Than 12 Months, Unrealized Losses	7,683	34,202
12 Months or Longer, Fair Value	114,763	149,895
12 Months or Longer, Unrealized Losses	11,534	6,680
Total, Fair Value	1,924,146	3,155,197
Total, Unrealized Losses	19,217	40,882
Tax exempt bonds
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	817,019	890,907
Less Than 12 Months, Unrealized Losses	1,927	2,264
12 Months or Longer, Fair Value	83	63,474
12 Months or Longer, Unrealized Losses	18	473
Total, Fair Value	817,102	954,381
Total, Unrealized Losses	1,945	2,737
Taxable bonds
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	956,713	1,676,719
Less Than 12 Months, Unrealized Losses	2,297	9,988
12 Months or Longer, Fair Value	51,490	70,309
12 Months or Longer, Unrealized Losses	875	411
Total, Fair Value	1,008,203	1,747,028
Total, Unrealized Losses	3,172	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
12 Months or Longer, Unrealized Losses	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	35,651	274,517
Less Than 12 Months, Unrealized Losses	3,459	20,561
12 Months or Longer, Fair Value	63,190	16,112
12 Months or Longer, Unrealized Losses	10,641	5,796
Total, Fair Value	98,841	290,629
Total, Unrealized Losses	$ 14,100	$ 26,357