DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES Narrative (Details) gal in Millions, MMBTU in Millions	May. 21, 2015 USD ($)	Aug. 06, 2014 USD ($)	Dec. 01, 2015 USD ($)	Sep. 30, 2015 USD ($) MMBTU $ / gal gal	Sep. 15, 2015 USD ($)	Apr. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Sep. 30, 2014 USD ($)	Aug. 19, 2014 USD ($)	Jul. 08, 2014 USD ($)
Derivative [Line Items]
Notional amount of non-exchange traded natural gas commodity contracts (in MMBtu) | MMBTU				104.7
Notional amount of non-exchange traded natural gas commodity contracts to be settled during fiscal 2016 | MMBTU				88.0
Notional amount of non-exchange traded natural gas commodity contracts to be settled during fiscal 2017 | MMBTU				14.9
Notional amount of non-exchange traded natural gas commodity to be settled during fiscal 2018 | MMBTU				1.7
Notional amount of non-exchange traded natural gas commodity to be settled during fiscal 2019 | MMBTU				0.1
Long-term debt issued amount									$ 625,000,000.0
Cash margin receivables not offset with derivatives				$ 5,900,000				$ 4,400,000
Cash Flow Hedging | Designated as Hedging Instrument | Interest Rate Swaps
Derivative [Line Items]
Notional amount										$ 375,000,000
Loss on termination and settlement of interest rate swap		$ 19,000,000
Laclede Gas
Derivative [Line Items]
Gasoline futures contracts notional amount (in gallons) | gal				1.8
Average price of future contracts (dollars per gallon) | $ / gal				1.63
MMBtu (millions) | MMBTU				20.3
Cash margin receivables not offset with derivatives				$ 5,900,000				$ 4,400,000
Alagasco
Derivative [Line Items]
Unsecured debt							$ 115,000,000.0
Alagasco | 3.21% Notes, due September 15, 2025
Derivative [Line Items]
Unsecured debt					$ 35,000,000.0
Alagasco | Notes 4.31%, Due December 1, 2045 | Scenario, Forecast
Derivative [Line Items]
Unsecured debt			$ 80,000,000.0
Alagasco | Designated as Hedging Instrument | Interest Rate Swaps
Derivative [Line Items]
Notional amount						$ 24,000,000	$ 80,500,000
Fixed interest rate, lower range							2.18%
Fixed interest rate, higher range							2.85%
Gain on settlement of derivative	$ 2,700,000