Available for Sale Securities (Detail) - USD ($) $ in Thousands	Sep. 24, 2016	Dec. 26, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 6,924,477	$ 6,551,908
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	145,321	91,908
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	19,217	40,882
Fair Value	7,050,581	6,602,934
Tax exempt bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,174,197	3,336,841
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	13,958	12,038
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1,945	2,737
Fair Value	3,186,210	3,346,142
Taxable bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,620,138	2,214,366
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	8,229	1,492
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	3,172	10,399
Fair Value	2,625,195	2,205,459
Restricted investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	164,549	164,548
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1,851	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	1,389
Fair Value	166,400	163,159
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	965,593	836,153
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	121,283	78,378
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	14,100	26,357
Fair Value	$ 1,072,776	$ 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
-Subparagraph (aa)
-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
-Paragraph 1
-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
-Paragraph 2
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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
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

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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
-Subparagraph (SX 210.5-02.2)
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