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Schedule of Unrealized Loss on Available-for-Sale Investments (Detail) - USD ($) $ in Thousands | Dec. 26, 2020 | Dec. 28, 2019
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Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value | $ 3,222 | $ 10,525
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss | 98 | 47
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value |  | 4,260
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss |  | 3
Available-for-sale investments with unrealized losses, Fair Value, Total | 3,222 | 14,785
Available-for-sale investments with unrealized losses, Unrealized Loss, Total | 98 | 50
Asset-backed securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value | 541 | 571
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss | 26 | 1
Available-for-sale investments with unrealized losses, Fair Value, Total | 541 | 571
Available-for-sale investments with unrealized losses, Unrealized Loss, Total | 26 | 1
Corporate bonds and direct obligations of government agencies |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value | 2,681 | 8,728
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss | 72 | 41
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value |  | 4,260
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss |  | 3
Available-for-sale investments with unrealized losses, Fair Value, Total | 2,681 | 12,988
Available-for-sale investments with unrealized losses, Unrealized Loss, Total | $ 72 | 44
U.S. Treasury obligations |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value |  | 1,226
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss |  | 5
Available-for-sale investments with unrealized losses, Fair Value, Total |  | 1,226
Available-for-sale investments with unrealized losses, Unrealized Loss, Total |  | $ 5

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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 No definition available. + 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27337-111563 + Details
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