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Schedule of Unrealized Loss on Available-for-Sale Investments (Detail) - USD ($) $ in Thousands | Dec. 30, 2017 | Dec. 31, 2016
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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 | $ 43,186 | $ 42,906
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss | 224 | 207
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value | 14,648 | 3,681
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss | 116 | 57
Available-for-sale investments with unrealized losses, Fair Value, Total | 57,834 | 46,587
Available-for-sale investments with unrealized losses, Unrealized Loss, Total | 340 | 264
Asset-backed securities |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Value | 1,864 | 1,363
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss | 4 | 6
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value | 632 | 2,314
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss | 1 | 13
Available-for-sale investments with unrealized losses, Fair Value, Total | 2,496 | 3,677
Available-for-sale investments with unrealized losses, Unrealized Loss, Total | 5 | 19
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 | 41,322 | 28,809
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss | 220 | 195
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Value | 14,016 | 1,367
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss | 115 | 44
Available-for-sale investments with unrealized losses, Fair Value, Total | 55,338 | 30,176
Available-for-sale investments with unrealized losses, Unrealized Loss, Total | $ 335 | 239
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
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss |  | 6
Available-for-sale investments with unrealized losses, Fair Value, Total |  | 12,734
Available-for-sale investments with unrealized losses, Unrealized Loss, Total |  | $ 6

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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=82897076&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=82897076&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 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=82897076&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=82897076&loc=d3e27337-111563 + Details
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