Marketable Securities (Schedule 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
Gross Unrealized Holding Gains	4,878	5,723
Gross Unrealized Holding Losses	(1,374)	(1,139)
Fair value	114,727	111,855
Equity Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Debt Securities, Available-for-sale [Line Items]
Equity securities, Fair Value	7,648	7,410
Corporate And Municipal Bonds [Member] \| Fair Value, Inputs, Level 2 [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	103,575	99,861
Gross Unrealized Holding Gains	4,878	5,723
Gross Unrealized Holding Losses	(1,374)	(1,139)
Fair Value	$ 107,079	$ 104,445

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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