Derivatives And Risk Management (Narrative) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Secured Debt	$ 1,426,700,000	$ 1,336,700,000
Cash deposited as collateral	23,800,000
Derivative, Fair Value, Amount Offset Against Collateral, Net	10,413,000	9,707,000
Liability position at aggregate fair value	23,300,000
Collateral agreements	18,500,000
Energy Derivative Contracts [Member]
Derivative [Line Items]
Letters of credit outstanding	20,100,000
First Mortgage [Member] | 2041 [Member]
Derivative [Line Items]
Secured Debt	$ 85,000,000	$ 85,000,000