DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES Narrative (Details) (USD $)				12 Months Ended		0 Months Ended
	Sep. 30, 2014 MMBTU	Aug. 19, 2014	Sep. 30, 2013	Sep. 30, 2014 Laclede Gas MMBTU gal	Sep. 30, 2013 Laclede Gas	Aug. 06, 2014 Designated as Hedging Instrument Cash Flow Hedging Interest Rate Swaps	Jul. 08, 2014 Designated as Hedging Instrument Cash Flow Hedging Interest Rate Swaps
Derivative [Line Items]
Maximum percentage of normal volumes hedged				70.00%
Maximum number of months normal volumes can be hedged				36 months
Gasoline futures contracts notional amount (in gallons)				1,800,000
Average price of future contracts (dollars per gallon)				2.60
Notional amount of non-exchange traded natural gas commodity contracts (in MMBtu)	33,500,000
Notional amount of non-exchange traded natural gas commodity contracts to be settled during fiscal 2015	32,100,000
Notional amount of non-exchange traded natural gas commodity contracts to be settled during fiscal 2016	1,400,000
Notional amount							$ 375,000,000
Loss on termination and settlement of interest rate swap						19,000,000
Long-term debt issued amount		625,000,000.0
MMBtu (millions)				21,000,000
Cash margin receivables not offset with derivatives	$ 4,600,000		$ 3,200,000	$ 4,400,000	$ 3,200,000