Accumulated Other Comprehensive Income (Schedule Of Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income and interest expense	$ 1,096	$ 657	$ 668	$ 1,893
Provision for income taxes	(4,431)	(2,402)	(17,594)	(21,295)
Net income	14,207	4,449	49,492	34,760
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		5	54	5
Provision for income taxes		(2)	(15)	(2)
Net income		$ 3	$ 39	$ 3