Accumulated Other Comprehensive Income (Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 25, 2016	Jun. 27, 2015	Jun. 25, 2016	Jun. 27, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income	$ 682	$ 585	$ 1,319	$ 1,117
Provision for income taxes	(9,474)	(9,507)	(21,252)	(16,581)
Net income	15,265	16,644	35,393	29,967
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	0	9	269	15
Provision for income taxes	0	(4)	(111)	(7)
Net income	$ 0	$ 5	$ 158	$ 8