Accumulated Other Comprehensive Income (Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2015	Jun. 28, 2014	Jun. 27, 2015	Jun. 28, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income	$ 585	$ 656	$ 1,117	$ 1,409
Provision for income taxes	(9,357)	(7,296)	(16,281)	(15,586)
Net income	16,430	12,798	29,539	27,564
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	9	5	15	46
Provision for income taxes	(4)	(2)	(7)	(20)
Net income	$ 5	$ 3	$ 8	$ 26