Accumulated Other Comprehensive Income (Schedule Of Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 29, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 30, 2017	[1]	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income and interest expense										$ (1,454)	$ 2,598	$ 2,457
Provision for income taxes										(19,398)	19,391	(37,499)
Net income	$ 13,245	$ 14,207	$ 19,095	$ 16,191	$ 63,654		$ 4,449	$ 18,475	$ 11,836	62,738	98,414	87,162
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										(54)	(40)	437
Provision for income taxes										14	11	(180)
Net income										$ (40)	$ (29)	$ 257

[1] The quarter ended December 30, 2017 includes the tax benefit of $49.3 million as a result of revaluing the Company's net deferred tax liability using the enacted Federal tax rate of 21% under the Tax Reform.