Benefit Plans (Schedule of Net Benefit Costs) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,799	$ 1,531
Interest cost	2,965	2,860
Expected return on assets	(3,034)	(3,328)
Amortization of prior service costs	97	98
Cumulative net loss	2,593	1,780
Net periodic pension/postretirement cost (benefit)	4,420	2,941
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	19	14
Interest cost	174	221
Amortization of prior service costs	(117)	0
Cumulative net loss	72	28
Net periodic pension/postretirement cost (benefit)	$ 148	$ 263