Benefits Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 27, 2015	Jun. 28, 2014	Jun. 27, 2015	Jun. 28, 2014
Pension Benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost	$ 228	$ 175	$ 500	$ 397
Interest cost	2,027	2,059	4,081	4,127
Expected return on plan assets	(2,655)	(3,201)	(5,309)	(6,402)
Amortization of net loss (gain)	656	189	1,370	377
Net periodic benefit cost (income)	256	(778)	642	(1,501)
Other Benefits [Member]
Components of net periodic benefit cost [Abstract]
Service cost	84	87	180	176
Interest cost	190	186	386	363
Amortization of prior service cost (credit)	1	(1)	3	(1)
Amortization of net loss (gain)	(16)	(45)	(13)	(109)
Net periodic benefit cost (income)	$ 259	$ 227	$ 556	$ 429