Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Benefit Plans (Textuals)
Contributions to qualified and non qualified pension plans			$ 13,780	$ 21,500
Pension Benefits [Member]
Components of net periodic benefit cost
Service cost	2,861	2,713	5,723	5,426
Interest cost	7,958	7,872	15,916	15,744
Expected return on plan assets	(10,206)	(10,184)	(20,411)	(20,367)
Amortization of prior service cost (benefit)	64	64	129	129
Recognized net actuarial loss	4,183	2,394	8,394	4,800
Net periodic pension benefit cost	4,860	2,859	9,751	5,732
Other Benefits [Member]
Components of net periodic benefit cost
Service cost	0	0	0	0
Interest cost	203	232	407	465
Expected return on plan assets	0	0	0	0
Amortization of prior service cost (benefit)	(129)	(129)	(258)	(258)
Recognized net actuarial loss	122	97	243	194
Net periodic pension benefit cost	$ 196	$ 200	$ 392	$ 401