Available for Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 26, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 6,691,140	$ 6,551,908
Gross Unrealized Gains	114,449	91,908
Gross Unrealized Losses	66,971	40,882
Fair Value	6,738,618	6,602,934
Tax exempt bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,036,060	3,336,841
Gross Unrealized Gains	2,211	12,038
Gross Unrealized Losses	24,649	2,737
Fair Value	3,013,622	3,346,142
Taxable bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,469,192	2,214,366
Gross Unrealized Gains	1,359	1,492
Gross Unrealized Losses	33,903	10,399
Fair Value	2,436,648	2,205,459
Restricted investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	164,548	164,548
Gross Unrealized Gains	0	0
Gross Unrealized Losses	463	1,389
Fair Value	164,085	163,159
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,021,340	836,153
Gross Unrealized Gains	110,879	78,378
Gross Unrealized Losses	7,956	26,357
Fair Value	$ 1,124,263	$ 888,174

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
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-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
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-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
-Paragraph 2
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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