Accumulated Other Comprehensive Income (Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2015	Sep. 27, 2014	Sep. 26, 2015	Sep. 27, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income (loss)	$ (422)	$ 357	$ 695	$ 1,766
Provision for income taxes	(6,371)	(6,456)	(22,952)	(21,767)
Net income	12,788	13,511	42,754	40,682
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 (loss)	0	0	15	47
Provision for income taxes	0	0	(7)	(21)
Net income	$ 0	$ 0	$ 8	$ 26