Pension and Other Postretirement Benefits (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pensions [Member]
Pension and other postretirement benefits expenses
Service cost	$ 1,613	$ 1,569
Interest cost	5,322	5,572
Expected return on plan assets	(8,033)	(7,900)
Amortization of prior service cost (credit)	211	275
Recognized losses	2,759	1,332
Net periodic benefit cost	1,872	848
Other Postretirement Benefits [Member]
Pension and other postretirement benefits expenses
Service cost	77	95
Interest cost	680	739
Amortization of prior service cost (credit)	(396)	(286)
Recognized losses	286	164
Net periodic benefit cost	$ 647	$ 712