Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 24, 2016	Sep. 26, 2015	Sep. 24, 2016	Sep. 26, 2015
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 10,628	$ 12,788	$ 46,021	$ 42,754
Other comprehensive income (loss) by component, net of tax:
Available-for-sale marketable securities Unrealized holding gains (losses) arising during period (Net of deferred taxes of $184 and $168, respectively for the 13 Weeks Ended and $738 and $243, respectively for the 39 Weeks Ended)	(303)	(241)	1,019	(350)
Reclassification adjustment for gains included in net income (Net of deferred taxes of $70 and $0, respectively for the 13 Weeks Ended and $181 and $7, respectively for the 39 Weeks Ended)	(99)	0	(257)	(8)
Other comprehensive income (loss), net of tax	(402)	(241)	762	(358)
Comprehensive income, net of tax	$ 10,226	$ 12,547	$ 46,783	$ 42,396