Accumulated Other Comprehensive Income (Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 24, 2016	Jun. 25, 2016	Mar. 26, 2016	Dec. 26, 2015	Sep. 26, 2015	Jun. 27, 2015	Mar. 28, 2015	Dec. 31, 2016	Dec. 26, 2015	Dec. 27, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment income and interest expense									$ 2,457	$ 1,552	$ 2,287
Provision for income taxes									(37,499)	(33,001)	(29,281)
Net income	$ 41,140	$ 10,628	$ 15,265	$ 20,129	$ 16,575	$ 12,788	$ 16,644	$ 13,323	87,162	59,330	54,381
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 and interest expense									437	27	63
Provision for income taxes									(180)	(11)	(26)
Net income									$ 257	$ 16	$ 37