Disclosures About Derivative Instruments and Hedging Activities Textual (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Derivative [Line Items]
Fair values of electric utility's forward purchase power agreements	$ 39,959	$ 30,321
Interest rate cash flow hedge loss to be reclassified during next 12 months, net	(805)
Restricted Cash in brokerage accounts	0	4,308
Interest rate cash flow hedge loss reclassified to earnings, net	(1,164)	(1,164)
Electric Utility electric transmission congestion [Member]
Derivative [Line Items]
Notional amount (in units)	189,700,000	208,600,000
Transmission organization controls movements of wholesale electricity in number of states (in states)	14
Gas Utility [Member]
Derivative [Line Items]
Notional amount (in units)	19,200,000	15,100,000
Maximum Length of Time Hedged in Price Risk Cash Flow Hedges	12 months
Electric Utility - Forward Contract [Member]
Derivative [Line Items]
Notional amount (in units)	570,400,000	788,600,000
Maximum Length of Time Hedged in Price Risk Cash Flow Hedges	20 months
Fair values of electric utility's forward purchase power agreements	9,207	8,655
Interest Rate Swap [Member]
Derivative [Line Items]
Underlying variable rate debt	173,000	173,000
Recorded loss amount included in Other Income, Net	$ (682)