Accumulated Other Comprehensive Income (Schedule Of Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2020	Jun. 29, 2019	Jun. 27, 2020	Jun. 29, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income (loss) and interest expense	$ 3,066	$ 1,079	$ (953)	$ 3,975
Provision for income taxes	(14,978)	(6,473)	(24,374)	(11,043)
Net income	41,472	20,475	68,161	34,780
Unrealized Gains On Available-For-Sale Marketable Securities [Member] | Reclassification Out Of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income (loss) and interest expense	8
Provision for income taxes	(2)
Net income	$ 6