Amortized Cost and Fair Value of Available-for-Sale Investments (Detail) - USD ($) $ in Thousands	Dec. 28, 2019	Dec. 29, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 116,181	$ 113,359
Gross Unrealized Gains	1,477	33
Gross Unrealized Losses	50	1,217
Fair Value	117,608	112,175
Money market investments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	15,691	11,714
Fair Value	15,691	11,714
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	572	624
Gross Unrealized Losses	1	4
Fair Value	571	620
Corporate bonds and direct obligations of government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	97,583	101,021
Gross Unrealized Gains	1,465	33
Gross Unrealized Losses	44	1,213
Fair Value	99,004	$ 99,841
U.S. Treasury obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,335
Gross Unrealized Gains	12
Gross Unrealized Losses	5
Fair Value	$ 2,342

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=118939692&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

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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=118939692&loc=d3e27161-111563

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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

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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 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

Reference 2: 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=118954083&loc=d3e26610-111562

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-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

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