Accumulated Other Comprehensive Income (Reclassifications out of Accumulated Other Comprehensive Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 28, 2015	Mar. 29, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income	$ 532	$ 753
Provision for income taxes	(6,924)	(8,290)
Net income	13,109	14,766
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income	6	41
Provision for income taxes	(3)	(18)
Net income	$ 3	$ 23