Benefit Obligations (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Pension Benefits [Member]
Net Periodic Benefit Cost/(Credit)
Service cost	$ 531	$ 472	$ 1,792
Interest cost	67,499	70,337	73,774
Expected return on plan assets	(67,965)	(71,464)	(76,802)
Amortization of prior service cost and transition asset	18	38	49
Amortization of net actuarial loss/(gain)	6,750	2,155	(94)
Special termination benefit	0	0	426
Other	54	0	0
Total benefit cost/(credit)	6,887	1,538	(855)
Post-retirement Benefits [Member]
Net Periodic Benefit Cost/(Credit)
Service cost	75	81	79
Interest cost	2,597	2,441	2,426
Expected return on plan assets	(4,128)	(4,597)	(4,877)
Amortization of prior service cost and transition asset	0	0	0
Amortization of net actuarial loss/(gain)	552	0	0
Special termination benefit	0	0	0
Other	0	0	(1,529)
Total benefit cost/(credit)	$ (904)	$ (2,075)	$ (3,901)