NOTES PAYABLE AND CREDIT AGREEMENTS - Laclede Gas' Short-term Borrowings (Details) (USD $)	12 Months Ended
	Sep. 30, 2014		Sep. 30, 2013
Short-term Debt [Line Items]
Weighted average borrowings outstanding	$ 82,300,000	[1]	$ 34,200,000	[1]
Weighted average interest rate	0.50%	[1]	0.30%	[1]
Minimum borrowing outstanding	0		0
Maximum borrowing outstanding	300,500,000.0		99,400,000.0
Short-term debt	287,100,000	[1]	74,000,000	[1]
Weighted average interest rate	0.50%	[1]	0.30%	[1]
Laclede Gas
Short-term Debt [Line Items]
Weighted average borrowings outstanding	141,000,000		63,400,000
Weighted average interest rate	0.30%		0.30%
Minimum borrowing outstanding	45,500,000.0		0
Maximum borrowing outstanding	272,100,000.0		160,500,000.0
Short-term debt	238,600,000		120,700,000
Weighted average interest rate	0.30%		0.30%
Laclede Gas | Commercial Paper
Short-term Debt [Line Items]
Weighted average borrowings outstanding	77,600,000		34,200,000
Weighted average interest rate	0.30%		0.30%
Minimum borrowing outstanding	0		0
Maximum borrowing outstanding	244,500,000.0		99,400,000.0
Short-term debt	238,600,000		74,000,000
Weighted average interest rate	0.30%		0.30%
Laclede Gas | Notes Payable to Related Party
Short-term Debt [Line Items]
Weighted average borrowings outstanding	63,400,000		29,200,000
Weighted average interest rate	0.30%		0.30%
Minimum borrowing outstanding	0		0
Maximum borrowing outstanding	189,000,000.0		91,700,000.0
Short-term debt	$ 0		$ 46,700,000
Weighted average interest rate	0.00%		0.30%

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