Investments - Additional Information (Detail)	3 Months Ended	9 Months Ended
Sep. 24, 2016 USD ($) AFS_security	Sep. 26, 2015 USD ($)	Sep. 24, 2016 USD ($) AFS_security	Sep. 26, 2015 USD ($)	Dec. 26, 2015 USD ($)
Investments, Debt and Equity Securities [Abstract]
Total realized gains on sales of AFS securities	$ 7,012,000	$ 29,620,000	$ 18,896,000	$ 73,542,000
Total realized losses on sales of AFS securities	$ 941,000	$ 15,092,000	$ 5,938,000	$ 20,771,000
Number of AFS securities issues contributing to total unrealized loss \| AFS_security	329		329
Total, unrealized Losses	$ 19,217,000		$ 19,217,000		$ 40,882,000

Number Of Investment Positions With Unrealized Losses

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- Definition

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27290-111563

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- Definition

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27357-111563

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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ References

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- References

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