SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Part 1 (Details) (USD $)	3 Months Ended		6 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012	Sep. 30, 2012
Related Party Transaction [Line Items]
Outstanding borrowings from Laclede Group under a revolving credit note	$ 0	$ 107,540,000	$ 0	$ 107,540,000	$ 37,125,000
Interest rate on the borrowings		0.30%		0.30%	0.20%
REVENUE RECOGNITION [Abstract]
Amounts of accrued unbilled revenues	33,300,000	13,000,000	33,300,000	13,000,000	11,600,000
GROSS RECEIPT TAXES [Abstract]
Gross receipts taxes recorded in utility operating revenues	17,200,000	15,500,000	27,500,000	25,700,000
STOCK-BASED COMPENSATION [Abstract]
Total equity compensation cost	974,000	582,000	1,506,000	1,149,000
Compensation cost capitalized	(356,000)	(221,000)	(539,000)	(359,000)
Compensation cost recognized in net income	618,000	361,000	967,000	790,000
Income tax benefit recognized in net income	(235,000)	(140,000)	(370,000)	(305,000)
Compensation cost recognized in net income, net of income tax	383,000	221,000	597,000	485,000
Total unrecognized compensation cost	6,000,000		6,000,000
Weighted average period allocation (in years)	2 years 2 months 13 days
Laclede Energy Resources, Inc. [Member]
Related Party Transaction [Line Items]
Description of transaction			sales of natural gas	sales of natural gas
Purchases from related parties			15,000,000	8,500,000
Revenue from related Parties			10,400,000
Laclede Pipeline Company [Member]
Related Party Transaction [Line Items]
Description of transaction			transportation services	transportation services
Purchases from related parties			$ 500,000	$ 500,000