Accumulated Other Comprehensive Income (Details 1) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2015	Sep. 27, 2014	Sep. 26, 2015	Sep. 27, 2014
Summary of reclassifications out of Accumulated Other Comprehensive Income
Amount Reclassified from AOCI, Unrealized gains and losses on available-for-sale securities, Total before tax	$ 12,543	$ 15,001	$ 41,874	$ 50,373
Amount Reclassified from AOCI, Unrealized gains and losses on available-for-sale securities, Tax benefit	(4,133)	(5,124)	(13,839)	(16,924)
Net income	$ 8,410	$ 9,877	28,035	$ 33,449
Reclassification out of Accumulated Other Comprehensive Income [Member]
Summary of reclassifications out of Accumulated Other Comprehensive Income
Net income			152
Unrealized gains and losses on available-for-sale securities [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Summary of reclassifications out of Accumulated Other Comprehensive Income
Amount Reclassified from AOCI, Unrealized gains and losses on available-for-sale securities, Total before tax			241
Amount Reclassified from AOCI, Unrealized gains and losses on available-for-sale securities, Tax benefit			(89)
Net income			152
Accumulated Other-than-Temporary Impairment [Member] | Unrealized gains and losses on available-for-sale securities [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Summary of reclassifications out of Accumulated Other Comprehensive Income
Amount Reclassified from AOCI, Unrealized gains and losses on available-for-sale securities, Realized gain/(loss) on sale of securities			$ 241