Employee Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 27, 2014	Sep. 28, 2013	Sep. 27, 2014	Sep. 28, 2013
Components of net periodic benefit costs:
Service cost	$ 333	$ 532	$ 999	$ 1,596
Interest cost	2,205	1,967	6,615	5,901
Expected return on plan assets	(1,756)	(1,629)	(5,268)	(4,887)
Amortization of net loss	821	1,147	2,463	3,441
Amortization of prior service cost	11	11	33	33
Net periodic benefit costs	$ 1,614	$ 2,028	$ 4,842	$ 6,084