Benefit 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 Benefits [Member]
Components of the net periodic benefit cost/(credit)
Service cost	$ 116	$ 141	$ 225	$ 275
Interest cost	15,483	16,929	30,735	33,779
Expected return on plan assets	(17,030)	(17,000)	(34,053)	(33,998)
Amortization of net actuarial loss, prior service cost and transition asset	3,693	1,699	7,162	3,385
Total benefit cost/(credit)	2,262	1,769	4,069	3,441
Post-retirement Benefits [Member]
Components of the net periodic benefit cost/(credit)
Service cost	20	21	45	38
Interest cost	643	621	1,293	1,246
Expected return on plan assets	(856)	(1,033)	(1,906)	(2,065)
Amortization of net actuarial loss, prior service cost and transition asset	490	85	990	177
Total benefit cost/(credit)	$ 297	$ (306)	$ 422	$ (604)