Derivatives And Risk Management (Narrative) (Details) (USD $)						1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Energy Derivative Contracts [Member]	Dec. 31, 2011 First Mortgage [Member] 2041 [Member]	Sep. 30, 2011 First Mortgage [Member] 2041 [Member]	Sep. 30, 2012 Interest Rate Swap [Member]	May 31, 2012 Interest Rate Swap [Member]	Sep. 30, 2011 Interest Rate Swap [Member]	May 31, 2012 Interest Rate Swap [Member] First Mortgage [Member]		Sep. 30, 2011 Interest Rate Swap [Member] First Mortgage [Member] 2041 [Member]
Derivative [Line Items]
Notional amount of interest rate derivatives							$ 75,000,000	$ 85,000,000
Cash received (paid) for settlement of interest rate swap agreements						10,600,000	18,500,000
Secured Debt	1,336,700,000	1,263,700,000		85,000,000	85,000,000				80,000,000	[1]	85,000,000
Cash deposited as collateral	10,100,000
Letters of credit outstanding			28,100,000
Derivative, Fair Value, Amount Offset Against Collateral, Net	9,707,000
Liability position at aggregate fair value	35,900,000
Collateral agreements	$ 25,800,000

[1] In November 2012, the Company issued $80.0 million of 4.23 percent First Mortgage Bonds due in 2047.