Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jul. 01, 2012	Jul. 03, 2011	Jul. 01, 2012	Jul. 03, 2011
Pension Plans [Member]
Components of net periodic pension costs
Service cost	$ 27	$ 25	$ 55	$ 50
Interest cost	3,123	3,085	6,247	6,170
Expected return on plan assets	(2,972)	(2,922)	(5,945)	(5,844)
Amortization of prior service cost	5	4	10	8
Recognized net actuarial loss	694	518	1,387	1,036
Net periodic cost	877	710	1,754	1,420
Postretirement Benefits [Member]
Components of net periodic pension costs
Service cost	316	242	632	484
Interest cost	782	708	1,563	1,416
Amortization of unrecognized transitional assets	0	(5)	0	(10)
Amortization of prior service cost	(379)	(429)	(758)	(858)
Recognized net actuarial loss	612	530	1,225	1,060
Net periodic cost	$ 1,331	$ 1,046	$ 2,662	$ 2,092