Pension and Other Post-Retirement Benefits Changes in Plan Assets and Benefit Obligations Recognized as a Regulatory Liability (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Other Postretirement Benefit Plans, Defined Benefit [Member]
Changes in Plan Assets and Benefit Obligations Recognized as a Regulatory Liability [Line Items]
Change in Net Loss (Gain) Recognized as Regulatory Asset (Liability)	$ (1,028)	$ 1,123
Change in Transition Obligation (Credit) Recognized as Regulatory Asset (Liability)	(10)	(2,433)
Amortization of Transition Obligation Recognized as Regulatory Asset (Liability)	0	0
Amortization of Prior Service Cost Recognized as Regulatory Asset (Liability)	806	665
Amortization of Net Loss Recognized as Regulatory Asset (Liability)	(615)	(613)
Total Recognized to Regulatory Asset	(847)	(1,258)
Pension Plans, Defined Benefit [Member]
Changes in Plan Assets and Benefit Obligations Recognized as a Regulatory Liability [Line Items]
Change in Net Loss (Gain) Recognized as Regulatory Asset (Liability)	6,254	8,550
Change Prior Service Cost Recognized as Regulatory Asset (Liability)	14	0
Amortization of Transition Obligation Recognized as Regulatory Asset (Liability)	0	(2)
Amortization of Prior Service Cost Recognized as Regulatory Asset (Liability)	(74)	(69)
Amortization of Net Loss Recognized as Regulatory Asset (Liability)	(1,753)	(687)
Total Recognized to Regulatory Asset	$ 4,441	$ 7,792