Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Benefit Plans (Textuals)
Contributions to qualified and non qualified pension plans	$ 12,864	$ 20,697
Pension Benefits [Member]
Components of net periodic benefit cost
Service cost	2,862	2,713
Interest cost	7,958	7,872
Expected return on plan assets	(10,205)	(10,183)
Amortization of prior service cost	65	65
Recognized net actuarial loss	4,211	2,406
Net periodic pension benefit cost	4,891	2,873
Other Benefits [Member]
Components of net periodic benefit cost
Service cost	0	0
Interest cost	204	233
Expected return on plan assets	0	0
Amortization of prior service cost	(129)	(129)
Recognized net actuarial loss	121	97
Net periodic pension benefit cost	$ 196	$ 201