NOTES PAYABLE AND CREDIT AGREEMENTS - Narrative (Details)		12 Months Ended
	Sep. 02, 2014 USD ($) bank	Sep. 30, 2016 USD ($) bank
Line of Credit Facility [Line Items]
Speculative interest rate increase percent		1.00%
Decrease in cash flow with an impact of 100 basis point interest rate increase		$ 2,700,000
Laclede Gas
Line of Credit Facility [Line Items]
Speculative interest rate increase percent		1.00%
Decrease in cash flow with an impact of 100 basis point interest rate increase		$ 2,200,000
Alagasco
Line of Credit Facility [Line Items]
Speculative interest rate increase percent		1.00%
Decrease in cash flow with an impact of 100 basis point interest rate increase		$ 400,000
Line of Credit
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity		$ 150,000,000.0
Banks in syndicated line of credit facility | bank		9
Minimum required ratio of earnings before interest, taxes, depreciation, and amortization (EBITDA) times interest expense as required by the line of credit covenant		70.00%
Debt to total capitalization ratio		0.585
Line of Credit | Laclede Gas
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity		$ 450,000,000.0
Banks in syndicated line of credit facility | bank		10
Minimum required ratio of earnings before interest, taxes, depreciation, and amortization (EBITDA) times interest expense as required by the line of credit covenant		70.00%
Debt to total capitalization ratio		0.497
Line of Credit | Alagasco
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity	$ 150,000,000.0
Banks in syndicated line of credit facility | bank	12
Minimum required ratio of earnings before interest, taxes, depreciation, and amortization (EBITDA) times interest expense as required by the line of credit covenant	70.00%
Debt to total capitalization ratio		0.278
Line of Credit | Liabilities | Lender Concentration Risk
Line of Credit Facility [Line Items]
Percent of debt by a singe bank		15.60%
Line of Credit | Liabilities | Lender Concentration Risk | Laclede Gas
Line of Credit Facility [Line Items]
Percent of debt by a singe bank		15.60%
Line of Credit | Liabilities | Lender Concentration Risk | Alagasco
Line of Credit Facility [Line Items]
Percent of debt by a singe bank	10.00%