Pension and Other Postretirement Obligations (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 Obligations [Member]
Components of net periodic benefit cost
Service cost	$ 1,432	$ 1,364	$ 2,864	$ 2,713
Interest cost	3,037	2,867	6,047	5,678
Amortization of prior service credit	(19)	(36)	(39)	(72)
Expected return on plan assets	(3,169)	(2,901)	(6,333)	(5,761)
Net loss recognition	1,490	1,545	2,982	3,088
Net periodic benefit cost	2,771	2,839	5,521	5,646
Other Postretirement Obligations [Member]
Components of net periodic benefit cost
Service cost	30	41	62	81
Interest cost	545	672	1,133	1,353
Amortization of prior service credit	(29)	(59)	(58)	(119)
Net loss recognition	223	111	485	230
Net periodic benefit cost	$ 769	$ 765	$ 1,622	$ 1,545