Marketable Securities (Schedule Of Maturities of Marketable Securities) (Details) - USD ($) $ in Thousands	Sep. 26, 2020	Dec. 28, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 91,013	$ 52,264
Marketable Securities, Excluding Equity Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost, Due within one year	10,561
Amortized Cost, Due after one year through five years	37,659
Amortized Cost, Due after five years through ten years	42,793
Amortized Cost	91,013
Fair Value, Due within one year	10,649
Fair Value, Due after one year through five years	39,421
Fair Value, Due after five years through ten years	45,071
Fair Value	$ 95,141

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

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Section 45
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