Benefit Plans (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Benefit Plans (Textuals)
Contributions to qualified and non qualified pension plans			$ 22,503	$ 14,673
Pension Benefits [Member]
Components of net periodic benefit cost
Service cost	2,713	2,500	8,139	7,498
Interest cost	7,873	7,680	23,617	23,042
Expected return on plan assets	(10,183)	(9,604)	(30,550)	(28,810)
Amortization of prior service cost	65	48	194	145
Recognized net actuarial loss	2,349	1,512	7,149	4,229
Net periodic pension benefit cost	2,817	2,136	8,549	6,104
Other Benefits [Member]
Components of net periodic benefit cost
Interest cost	233	249	698	745
Amortization of prior service cost	(130)	(130)	(388)	(388)
Recognized net actuarial loss	98	71	292	213
Net periodic pension benefit cost	$ 201	$ 190	$ 602	$ 570