Other Postretirement Benefits (Details) - Other Postretirement Benefit Plan - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2015	Sep. 28, 2014	Sep. 27, 2015	Sep. 28, 2014
Pension Benefits
Service cost	$ 148	$ 145	$ 442	$ 439
Interest cost	688	930	2,065	2,950
Amortization of actuarial loss	1,303	1,237	3,909	3,605
Amortization of prior service credit	(2,399)	(1,800)	(7,349)	(5,000)
Net periodic pension cost	$ (260)	$ 512	$ (933)	$ 1,994