Accumulated Other Comprehensive Income (Schedule Of Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 28, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 29, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income and interest expense									$ 7,054	$ (1,454)	$ 2,598
Provision for income taxes									(20,661)	(19,398)	19,391
Net income	$ 18,885	$ 14,319	$ 20,475	$ 14,304	$ 13,245	$ 14,207	$ 19,095	$ 16,191	67,983	62,738	98,414
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 and interest expense									(51)	(54)	(40)
Provision for income taxes									14	14	11
Net income									$ (37)	$ (40)	$ (29)