Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 30, 2017	Sep. 24, 2016
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 4,449	$ 10,628	$ 34,760	$ 46,021
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 $194 and $184, respectively for the 13 Weeks Ended and $68 and $738, respectively for the 39 Weeks Ended)	281	(303)	147	1,019
Reclassification adjustment for (gains) losses included in net income (Net of deferred taxes of $2 and $70, respectively for the 13 Weeks Ended and $2 and $181, respectively for the 39 Weeks Ended	3	(99)	3	(257)
Other comprehensive income, net of tax	284	(402)	150	762
Comprehensive income, net of tax	$ 4,733	$ 10,226	$ 34,910	$ 46,783