NOTES PAYABLE AND CREDIT AGREEMENTS - Narrative (Details) (USD $)	12 Months Ended										12 Months Ended			0 Months Ended	12 Months Ended				0 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014 Laclede Gas	Sep. 30, 2013 Laclede Gas	Sep. 30, 2014 Line of Credit bank	Sep. 30, 2013 Line of Credit	Sep. 02, 2014 Line of Credit	Sep. 30, 2014 Line of Credit Laclede Gas bank	Sep. 30, 2014 Line of Credit Alagasco		Sep. 02, 2014 Line of Credit Alagasco bank	Sep. 03, 2014 Notes Payable to Related Party Laclede Gas	Sep. 30, 2014 Notes Payable to Related Party Laclede Gas	Sep. 30, 2013 Notes Payable to Related Party Laclede Gas	Sep. 30, 2014 Liabilities Lender Concentration Risk Line of Credit	Sep. 30, 2014 Liabilities Lender Concentration Risk Line of Credit Laclede Gas	Sep. 02, 2014 Liabilities Lender Concentration Risk Line of Credit Alagasco
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity									$ 150,000,000	$ 450,000,000.0
Banks in syndicated line of credit facility							9			9			12
Percent of debt by a singe bank																	15.60%	15.60%	10.00%
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%			70.00%			70.00%
Debt to total capitalization ratio							0.59			0.51	0.24
Extension period under credit agreement														1 year
Minimum borrowing outstanding	0		0		45,500,000.0	0	0	0			9,000,000.0	[1]			0	0
Maximum borrowing outstanding	300,500,000.0		99,400,000.0		272,100,000.0	160,500,000.0	40,000,000	0			16,000,000.0	[1]			189,000,000.0	91,700,000.0
Short-term debt	287,100,000	[2]	74,000,000	[2]	238,600,000	120,700,000	32,500,000	0			16,000,000	[1]			0	46,700,000
Decrease in cash flow with an impact of 100 basis point interest rate increase	$ 800,000

[1] Weighted average borrowings for Alagasco represents Laclede Group's ownership period of one month. The one month average approximates the Alagasco daily outstanding balance for the fiscal year ended September 30, 2014.

[2] Represents twelve month weighted average for Laclede Group, Laclede Gas, and Alagasco.