Amortized Cost and Fair Value of Available-for-Sale Investments (Detail) - USD ($) $ in Thousands	Sep. 29, 2018	Dec. 30, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 112,991	$ 111,142
Gross Unrealized Gains	15	117
Gross Unrealized Losses	1,314	340
Fair Value	111,692	110,919
Money market investments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	12,430	27,895
Fair Value	12,430	27,895
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	728	2,805
Gross Unrealized Losses	5	5
Fair Value	723	2,800
Corporate bonds and direct obligations of government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	99,833	80,442
Gross Unrealized Gains	15	117
Gross Unrealized Losses	1,309	335
Fair Value	$ 98,539	$ 80,224

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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- Definition

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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- Definition

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

No definition available.

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- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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