Benefit Plans (Schedule of Net Benefit Costs) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 54	$ 61
Interest cost	886	959
Curtailment gain			(10,200)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	6,123	5,919	5,290
Interest cost	11,439	11,200	11,003
Expected return on assets	(13,313)	(12,059)	(11,222)
Prior service cost	394	394	392
Cumulative net loss	7,120	5,708	3,031
Curtailment gain	0	0	0
Net periodic pension/postretirement cost (benefit)	11,763	11,162	8,494
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	54	61	173
Interest cost	886	959	1,412
Expected return on assets	0	0	0
Prior service cost	0	0	(90)
Cumulative net loss	114	15	63
Curtailment gain	0	0	(10,239)
Net periodic pension/postretirement cost (benefit)	$ 1,054	$ 1,035	$ (8,681)