Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pension Benefits [Member]
Components of Net Periodic Benefit Cost
Service cost	$ 5,587	$ 5,190
Interest cost	10,798	10,542
Expected return on plan assets	(12,195)	(12,370)
Amortization of prior service cost (credit)	69	85
Amortization of actuarial loss	4,882	2,824
Net periodic benefit cost	9,141	6,271
Pretax reclassification from AOCI included in net periodic benefit cost	4,951	2,909
Other Postretirement Benefits [Member]
Components of Net Periodic Benefit Cost
Service cost	1,166	1,197
Interest cost	1,562	1,613
Amortization of prior service cost (credit)	(169)	(169)
Amortization of actuarial loss	287	287
Net periodic benefit cost	2,846	2,928
Pretax reclassification from AOCI included in net periodic benefit cost	$ 118	$ 118