INCOME TAXES - Narrative (Details) - USD ($)	Sep. 30, 2016	Sep. 30, 2015
Tax Credit Carryforward [Line Items]
Federal and state loss carryforwards	$ 297,000,000
Contribution carryforwards	12,200,000
Valuation allowance	900,000	$ 0
Tax credit carryforwards	3,500,000
Unrecognized tax benefits affect on the Company's effective tax rate	3,300,000	3,100,000
Income taxes accrued	0	0
income tax penalties accrued	0
Laclede Gas
Tax Credit Carryforward [Line Items]
Federal and state loss carryforwards	105,000,000
Contribution carryforwards	12,000,000
Valuation allowance	900,000	0
Tax credit carryforwards	2,000,000
Unrecognized tax benefits affect on the Company's effective tax rate	3,100,000	2,900,000
Income taxes accrued	0	0
income tax penalties accrued	0	$ 0
Alagasco
Tax Credit Carryforward [Line Items]
Federal and state loss carryforwards	$ 159,000,000