Accumulated Other Comprehensive Income (Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 26, 2016	Mar. 28, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income	$ 637	$ 532
Provision for income taxes	(11,778)	(7,074)
Net income	20,129	13,323
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income	269	6
Provision for income taxes	(111)	(3)
Net income	$ 158	$ 3