SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Part 1 (Details) (USD $)	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013	Sep. 30, 2013
Related Party Transaction [Line Items]
Revenue from related parties			$ 7,800,000
Notes payable external and associated companies	113,400,000.000000000		113,400,000.000000000
Outstanding borrowings from Laclede Group under a revolving credit note	77,366,000	0	77,366,000	0	46,729,000
Interest rate on the borrowings	0.30%		0.30%
REVENUE RECOGNITION [Abstract]
Amounts of accrued unbilled revenues	77,100,000	33,300,000	77,100,000	33,300,000	25,200,000
GROSS RECEIPT TAXES [Abstract]
Gross receipts taxes recorded in utility operating revenues	34,300,000	17,200,000	54,300,000	27,500,000
STOCK-BASED COMPENSATION [Abstract]
Total equity compensation cost	1,675,000	974,000	2,132,000	1,506,000
Compensation cost capitalized	(556,000)	(356,000)	(705,000)	(539,000)
Compensation cost recognized in net income	1,119,000	618,000	1,427,000	967,000
Total unrecognized compensation cost	8,300,000		8,300,000
Weighted average period allocation (in years)	2 years 2 months 0 days
Laclede Energy Resources, Inc. [Member]
Related Party Transaction [Line Items]
Purchases from related parties			44,400,000	15,000,000
Revenue from related parties			4,300,000	10,400,000
Laclede Pipeline Company [Member]
Related Party Transaction [Line Items]
Purchases from related parties		$ 300,000	$ 900,000	$ 500,000