NOTES PAYABLE AND CREDIT AGREEMENTS - Laclede Group's 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]
Line of Credit
Short-term Debt [Line Items]
Weighted average borrowings outstanding	3,600,000		0
Weighted average interest rate	1.40%		0.00%
Minimum borrowing outstanding	0		0
Maximum borrowing outstanding	40,000,000		0
Short-term debt	32,500,000		0
Weighted average interest rate	1.40%		0.00%
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%
Alagasco | Line of Credit
Short-term Debt [Line Items]
Weighted average borrowings outstanding	13,200,000	[2]
Weighted average interest rate	1.20%	[2]
Minimum borrowing outstanding	9,000,000.0	[2]
Maximum borrowing outstanding	16,000,000.0	[2]
Short-term debt	$ 16,000,000	[2]
Weighted average interest rate	1.20%	[2]

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

[2] 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.