Disclosures About Derivative Instruments and Hedging Activities Textual (Details) (USD $) In Thousands, unless otherwise specified												3 Months Ended	6 Months Ended
	Mar. 31, 2013	Sep. 30, 2012	Mar. 31, 2012	Mar. 31, 2013 Electric Utility electric transmission congestion [Member] kWh	Mar. 31, 2012 Electric Utility electric transmission congestion [Member] kWh	Mar. 31, 2013 Gas Utility [Member] DTH	Mar. 31, 2012 Gas Utility [Member] DTH	Mar. 31, 2013 Electric Utility [Member] kWh	Mar. 31, 2012 Electric Utility [Member] kWh	Mar. 31, 2013 Interest Rate Protection Agreements [Member]	Mar. 31, 2012 Interest Rate Protection Agreements [Member]	Mar. 31, 2012 Interest Rate Swap [Member]	Mar. 31, 2012 Interest Rate Swap [Member]	Mar. 31, 2013 Derivative financial instruments [Member] Derivatives Designated as Hedging Instruments [Member] Interest rate contracts [Member]	Mar. 31, 2012 Derivative financial instruments [Member] Derivatives Designated as Hedging Instruments [Member] Interest rate contracts [Member]	Mar. 31, 2013 Derivative financial instruments [Member] Derivatives Subject to Utility Rate Regulation [Member] Commodity contracts [Member]	Mar. 31, 2012 Derivative financial instruments [Member] Derivatives Subject to Utility Rate Regulation [Member] Commodity contracts [Member]	Mar. 31, 2013 Derivative financial instruments [Member] Derivatives Not Designated as Hedging Instruments [Member] Commodity contracts [Member]	Mar. 31, 2012 Derivative financial instruments [Member] Derivatives Not Designated as Hedging Instruments [Member] Commodity contracts [Member]	Mar. 31, 2013 Derivative Financial Instruments, Liabilities [Member] Derivatives Designated as Hedging Instruments [Member] Interest rate contracts [Member]	Mar. 31, 2012 Derivative Financial Instruments, Liabilities [Member] Derivatives Designated as Hedging Instruments [Member] Interest rate contracts [Member]	Mar. 31, 2013 Derivative financial instruments and other noncurrent liabilities [Member] Derivatives Subject to Utility Rate Regulation [Member] Commodity contracts [Member]	Mar. 31, 2012 Derivative financial instruments and other noncurrent liabilities [Member] Derivatives Subject to Utility Rate Regulation [Member] Commodity contracts [Member]	Mar. 31, 2013 Electric Utility Electric Supply Contracts [Member]	Sep. 30, 2012 Electric Utility Electric Supply Contracts [Member]	Mar. 31, 2012 Electric Utility Electric Supply Contracts [Member]
Disclosures About Derivative Instruments Hedging Activities (Textual) [Abstract]
Notional amount (in units)				47,500,000	52,200,000	10,000,000	11,600,000	403,200,000	707,400,000
Total Derivatives Liability	$ (29,765)		$ (35,247)					$ 5,458	$ 14,747									$ 0	$ 0	$ 24,298	$ 17,345	$ 5,467	$ 17,902	$ (5,458)	$ (9,207)	$ (14,747)
Total Derivatives Assets	8,528		185											4,229	0	4,130	1	169	184
Underlying variable rate debt										173,000	173,000
Recorded loss amount included in Other Income, Net												(682)	682
Maximum length of time hedged in price risk cash flow hedges (in months)				2 months		12 months		14 months
Amount of net losses associated with interest rate hedges to be reclassified with interest rate hedges during the next 12 months	1,179
Restricted Cash in brokerage accounts	$ 0	$ 0	$ 4,260