Employee Benefit Plans (Details) - Components of other postretirement benefit cost - Other Postretirement Benefit Plan [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2015	Sep. 27, 2014	Sep. 26, 2015	Sep. 27, 2014
Employee Benefit Plans (Details) - Components of other postretirement benefit cost [Line Items]
Interest cost	$ 70	$ 75	$ 210	$ 224
Amortization of prior service benefit	(23)	(38)	(69)	(115)
Amortization of actuarial loss	29	18	87	56
Net periodic postretirement benefit cost	$ 76	$ 55	$ 228	$ 165