Marketable Securities (Schedule Of Marketable Securities) (Details) - USD ($) $ in Thousands	Dec. 26, 2020	Dec. 28, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 99,861	$ 52,264
Gross Unrealized Holding Gains	5,723	2,091
Gross Unrealized Holding Losses	(1,139)	(18)
Fair Value	104,445
Fair value	111,855	63,538
Equity Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Debt Securities, Available-for-sale [Line Items]
Equity securities, Fair Value	7,410	9,201
Corporate And Municipal Bonds [Member] \| Fair Value, Inputs, Level 2 [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	99,861	52,264
Gross Unrealized Holding Gains	5,723	2,091
Gross Unrealized Holding Losses	(1,139)	(18)
Fair Value	$ 104,445	$ 54,337

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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