Accumulated Other Comprehensive Income (Schedule Of Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income and interest expense	$ 1,467	$ 1,096	$ 5,441	$ 668
Provision for income taxes	(4,652)	(4,431)	(15,696)	(17,594)
Net income	14,319	14,207	49,098	49,492
Unrealized Gain 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 and interest expense	(55)		(55)	54
Provision for income taxes	16		16	(15)
Net income	$ (39)		$ (39)	$ 39