Marketable Securities (Schedule Of Maturities Of Marketable Securities) (Details) - USD ($) $ in Thousands	Mar. 27, 2021	Dec. 26, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 103,575	$ 99,861
Marketable Securities, Excluding Equity Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost, Due within one year	6,631
Amortized Cost, Due after one year through five years	44,550
Amortized Cost, Due after five years through ten years	52,394
Amortized Cost	103,575
Fair Value, Due within one year	6,675
Fair Value, Due after one year through five years	46,223
Fair Value, Due after five years through ten years	54,181
Fair Value	$ 107,079

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
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-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 45
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 210
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