INCOME TAXES (Details) - USD ($) $ in Millions	Sep. 30, 2015	Sep. 30, 2014	Aug. 31, 2014
Tax Credit Carryforward [Line Items]
Federal and state loss carryforwards	$ 123.9
Contribution carryforwards	11.0
Tax credit carryforwards	2.8
Unrecognized tax benefits affect on the Company's effective tax rate	3.1	$ 2.5
Laclede Gas
Tax Credit Carryforward [Line Items]
Federal and state loss carryforwards	10.0
Contribution carryforwards	10.9
Tax credit carryforwards	1.5
Unrecognized tax benefits affect on the Company's effective tax rate	2.9	$ 2.1
Alagasco
Tax Credit Carryforward [Line Items]
Federal and state loss carryforwards	$ 85.0
Alagasco
Tax Credit Carryforward [Line Items]
Percentage of voting interest acquired			100.00%