Benefit Plans (Schedule of Net Benefit Costs) (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
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,799	$ 1,531	$ 3,598	$ 3,062
Interest cost	2,965	2,860	5,930	5,720
Expected return on assets	(3,034)	(3,328)	(6,068)	(6,656)
Amortization of prior service costs	97	98	194	196
Cumulative net loss	2,593	1,780	5,186	3,560
Net periodic pension/postretirement cost (benefit)	4,420	2,941	8,840	5,882
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	19	14	38	28
Interest cost	174	221	348	442
Amortization of prior service costs	(117)	0	(234)	0
Cumulative net loss	72	28	144	56
Net periodic pension/postretirement cost (benefit)	$ 148	$ 263	$ 296	$ 526