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Schedule of Unrealized Loss on Available for Sale Investments (Detail) - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 26, 2015
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Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value | $ 42,906 | $ 58,791
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss | 207 | 288
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value | 3,681 | 562
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss | 57 | 53
Available-for-sale investments with unrealized losses, Fair Value, Total | 46,587 | 59,353
Available-for-sale investments with unrealized losses, Unrealized Loss, Total | 264 | 341
Asset-backed securities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value | 1,363 | 4,422
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss | 6 | 58
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value | 2,314 |
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss | 13 |
Available-for-sale investments with unrealized losses, Fair Value, Total | 3,677 | 4,422
Available-for-sale investments with unrealized losses, Unrealized Loss, Total | 19 | 58
Corporate bonds and direct obligations of government agencies |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value | 28,809 | 39,276
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss | 195 | 217
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value | 1,367 | 562
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss | 44 | 53
Available-for-sale investments with unrealized losses, Fair Value, Total | 30,176 | 39,838
Available-for-sale investments with unrealized losses, Unrealized Loss, Total | 239 | 270
U.S. Treasury Obligations |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value | 12,734 | 15,093
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss | 6 | 13
Available-for-sale investments with unrealized losses, Fair Value, Total | 12,734 | 15,093
Available-for-sale investments with unrealized losses, Unrealized Loss, Total | $ 6 | $ 13

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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer. + References Reference 1: 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 Reference 2: 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 + Details
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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 + Details
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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months. + References Reference 1: 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 Reference 2: 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 + Details
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