INCOME TAXES - Effective Income Tax Rate Variation from Stated Tax Rate (Details)	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Income Tax Contingency [Line Items]
Federal income tax statutory rate	35.00%	35.00%	35.00%
State and local income taxes, net of federal income tax benefits	1.80%	3.50%	2.90%
Certain expenses capitalized on books and deducted on tax return	(4.90%)	(9.70%)	(6.90%)
Taxes related to prior years	(0.70%)	(1.60%)	(0.80%)
Other items – net	(3.60%)	(2.20%)	(0.60%)
Effective income tax rate	27.60%	25.00%	29.60%
Laclede Gas
Income Tax Contingency [Line Items]
Federal income tax statutory rate	35.00%	35.00%	35.00%
State and local income taxes, net of federal income tax benefits	1.80%	3.30%	2.60%
Certain expenses capitalized on books and deducted on tax return	(4.50%)	(10.80%)	(8.90%)
Taxes related to prior years	(0.70%)	(1.60%)	(0.60%)
Other items – net	(3.30%)	(2.80%)	(1.10%)
Effective income tax rate	28.30%	23.10%	27.00%