Benefit Plans (Schedule of Net Benefit Costs) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,799	$ 1,531	$ 5,397	$ 4,593
Interest cost	2,965	2,860	8,895	8,580
Expected return on assets	(3,034)	(3,328)	(9,102)	(9,984)
Amortization of prior service costs	97	98	291	294
Cumulative net loss	2,593	1,780	7,779	5,340
Net periodic pension/postretirement cost (benefit)	4,420	2,941	13,260	8,823
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	19	14	57	42
Interest cost	174	221	522	663
Amortization of prior service costs	(117)	0	(351)	0
Cumulative net loss	72	28	216	84
Net periodic pension/postretirement cost (benefit)	$ 148	$ 263	$ 444	$ 789