DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Exchange-Traded/Cleared Derivatives (Details) MMBTU in Thousands	Sep. 30, 2015 MMBTU $ / MMBTU $ / gal
Laclede Gas
Derivative [Line Items]
MMBtu (millions)	20,300
Avg. Price Per MMBtu | $ / gal	1.63
Gas Utility | Natural gas contracts | Fiscal 2016 | Open Short Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu | $ / MMBTU	0.00
Gas Utility | Natural gas contracts | Fiscal 2016 | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	29,020
Avg. Price Per MMBtu | $ / MMBTU	3.19
Gas Utility | Natural gas contracts | Fiscal 2017 | Open Short Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu | $ / MMBTU	0.00
Gas Utility | Natural gas contracts | Fiscal 2017 | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	1,570
Avg. Price Per MMBtu | $ / MMBTU	3.04
Gas Utility | Natural gas contracts | Fiscal 2018 | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu | $ / MMBTU	0.00
Gas Utility | ICE Open basis swap positions | Fiscal 2016 | Open Short Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu | $ / MMBTU	0.00
Gas Utility | ICE Open basis swap positions | Fiscal 2016 | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu | $ / MMBTU	0.00
Gas Utility | ICE Open basis swap positions | Fiscal 2017 | Open Short Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu | $ / MMBTU	0.00
Gas Utility | ICE Open basis swap positions | Fiscal 2017 | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu | $ / MMBTU	0.00
Gas Utility | ICE Open basis swap positions | Fiscal 2018 | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu | $ / MMBTU	0.00
Gas Utility | OTC Open long futures/swap positions | Fiscal 2016 | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	4,430
Avg. Price Per MMBtu | $ / MMBTU	3.99
Gas Utility | OTC Open long futures/swap positions | Fiscal 2017 | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	320
Avg. Price Per MMBtu | $ / MMBTU	3.64
Gas Marketing | Natural gas contracts | Fiscal 2016 | Open Short Futures Positions
Derivative [Line Items]
MMBtu (millions)	13,340
Avg. Price Per MMBtu | $ / MMBTU	3.26
Gas Marketing | Natural gas contracts | Fiscal 2016 | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	7,060
Avg. Price Per MMBtu | $ / MMBTU	3.17
Gas Marketing | Natural gas contracts | Fiscal 2017 | Open Short Futures Positions
Derivative [Line Items]
MMBtu (millions)	2,130
Avg. Price Per MMBtu | $ / MMBTU	3.42
Gas Marketing | Natural gas contracts | Fiscal 2017 | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	2,770
Avg. Price Per MMBtu | $ / MMBTU	3.43
Gas Marketing | Natural gas contracts | Fiscal 2018 | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	120
Avg. Price Per MMBtu | $ / MMBTU	3.37
Gas Marketing | ICE Open basis swap positions | Fiscal 2016 | Open Short Futures Positions
Derivative [Line Items]
MMBtu (millions)	10,620
Avg. Price Per MMBtu | $ / MMBTU	0.17
Gas Marketing | ICE Open basis swap positions | Fiscal 2016 | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	23,290
Avg. Price Per MMBtu | $ / MMBTU	0.27
Gas Marketing | ICE Open basis swap positions | Fiscal 2017 | Open Short Futures Positions
Derivative [Line Items]
MMBtu (millions)	1,400
Avg. Price Per MMBtu | $ / MMBTU	0.20
Gas Marketing | ICE Open basis swap positions | Fiscal 2017 | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	9,040
Avg. Price Per MMBtu | $ / MMBTU	0.45
Gas Marketing | ICE Open basis swap positions | Fiscal 2018 | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	1,090
Avg. Price Per MMBtu | $ / MMBTU	0.50
Gas Marketing | OTC Open long futures/swap positions | Fiscal 2016 | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu | $ / MMBTU	0.00
Gas Marketing | OTC Open long futures/swap positions | Fiscal 2017 | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu | $ / MMBTU	0.00