Accumulated Other Comprehensive Income (Schedule Of Accumulated Other Comprehensive Income) (Details) - Unrealized Gains (Losses) On Available-For-Sale Marketable Securities [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 26, 2020	Dec. 28, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income balance, beginning balance	$ 1,480	$ 262
Other comprehensive income before reclassifications	1,806	1,255
Amounts reclassified from accumulated other comprehensive income		(37)
Net current period change in other comprehensive income	1,806	1,218
Accumulated other comprehensive income balance, ending balance	$ 3,286	$ 1,480