SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Part 1 (Details) (USD $)	3 Months Ended		9 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Sep. 30, 2011
Related Party Transaction [Line Items]
Outstanding borrowings from Laclede Group under a revolving credit note	$ 91,756,000	$ 32,502,000	$ 91,756,000	$ 32,502,000	$ 52,879,000
Interest rate on the borrowings	0.30%	0.30%	0.30%	0.30%	0.30%
REVENUE RECOGNITION [Abstract]
Amounts of accrued unbilled revenues	9,000,000	9,600,000	9,000,000	9,600,000	11,800,000
GROSS RECEIPT TAXES [Abstract]
Gross receipts taxes recorded in utility operating revenues	5,700,000	7,500,000	31,400,000	39,100,000
STOCK-BASED COMPENSATION [Abstract]
Total equity compensation cost	576,000	1,325,000	1,725,000	2,637,000
Compensation cost capitalized	(230,000)	(371,000)	(589,000)	(702,000)
Compensation cost recognized in net income	346,000	954,000	1,136,000	1,935,000
Income tax benefit recognized in net income	(133,000)	(367,000)	(438,000)	(746,000)
Compensation cost recognized in net income, net of income tax	213,000	587,000	698,000	1,189,000
Total unrecognized compensation cost	4,000,000		4,000,000
Weighted average period allocation (in years)			2 years 3 months 18 days
Laclede Energy Resources, Inc. [Member]
Related Party Transaction [Line Items]
Description of transaction	Sales of natural gas	Sales of natural gas	Sales of natural gas	Sales of natural gas
Purchases from related parties	1,800,000	6,500,000	10,300,000	19,100,000
Revenue from related Parties	1,200,000	0	1,200,000	1,600,000
Laclede Pipeline Company [Member]
Related Party Transaction [Line Items]
Description of transaction	Transportation services	Transportation services	Transportation services	Transportation services
Purchases from related parties	$ 300,000	$ 300,000	$ 800,000	$ 800,000