SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) (USD $)
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12 Months Ended | 0 Months Ended | 1 Months Ended | 12 Months Ended | 0 Months Ended | 12 Months Ended | 0 Months Ended | |||||||||||||||||||||
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Sep. 30, 2014
change
Operating_Segment
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Sep. 30, 2013
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Sep. 30, 2012
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Sep. 30, 2014
Laclede Gas
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Sep. 30, 2013
Laclede Gas
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Sep. 30, 2012
Laclede Gas
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Sep. 01, 2013
Laclede Gas
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Jun. 01, 2010
Alagasco
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Sep. 30, 2014
Alagasco
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Sep. 30, 2014
Alagasco
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Sep. 30, 2013
Alagasco
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Jun. 01, 2010
Alagasco
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Sep. 30, 2014
Missouri Gas Energy (MGE)
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Sep. 30, 2013
Missouri Gas Energy (MGE)
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Sep. 01, 2013
Missouri Gas Energy (MGE)
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Sep. 01, 2013
Missouri Gas Energy (MGE)
Laclede Gas
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Sep. 30, 2014
Missouri Gas Energy (MGE)
Laclede Gas
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Sep. 30, 2013
Missouri Gas Energy (MGE)
Laclede Gas
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Sep. 02, 2014
Alagasco
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Aug. 31, 2014
Alagasco
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Sep. 30, 2013
Alagasco
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Sep. 01, 2013
Alagasco
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Sep. 30, 2014
Alagasco
Laclede Gas
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Sep. 30, 2013
Alagasco
Laclede Gas
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Sep. 01, 2013
Scenario, Previously Reported
Missouri Gas Energy (MGE)
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Sep. 01, 2013
Scenario, Previously Reported
Missouri Gas Energy (MGE)
Laclede Gas
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Sep. 30, 2014
Gas Utility
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Sep. 30, 2013
Gas Utility
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Related Party Transaction [Line Items] | ||||||||||||||||||||||||||||
Number of operating segments | 3 | |||||||||||||||||||||||||||
Utility Plant, Depreciation and Amortization [Abstract] | ||||||||||||||||||||||||||||
Average annual depreciation and amortization expense percentage | 3.00% | 3.20% | 3.10% | |||||||||||||||||||||||||
Capital expenditures | $ 171,000,000 | $ 130,800,000 | $ 108,800,000 | $ 163,000,000 | $ 128,500,000 | $ 106,700,000 | $ 7,700,000 | |||||||||||||||||||||
Accruals for capital expenditures | 3,000,000 | 4,700,000 | 9,700,000 | 5,000,000 | ||||||||||||||||||||||||
Composite depreciation rate (percent) | 3.10% | |||||||||||||||||||||||||||
Current refundable negative salvage costs to customers | 13,400,000 | |||||||||||||||||||||||||||
Noncurrent refundable negative salvage costs to customers | 26,800,000 | |||||||||||||||||||||||||||
Noncurrent refundable negative salvage costs period (in years) | 5 years | |||||||||||||||||||||||||||
The amount by which the replacement cost exceeds (less than) the cost basis value of stored gas inventories | 11,400,000 | 13,300,000 | ||||||||||||||||||||||||||
Goodwill | 937,800,000 | 247,100,000 | 210,200,000 | 247,100,000 | 210,200,000 | 210,200,000 | 247,100,000 | 210,200,000 | 210,200,000 | 247,100,000 | 727,600,000 | 0 | 727,600,000 | 0 | 0 | 247,100,000 | 247,100,000 | |||||||||||
Total consideration transferred | 940,200,000 | 940,200,000 | 1,600,000,000 | |||||||||||||||||||||||||
Accrued unbilled revenues | 29,400,000 | 26,700,000 | ||||||||||||||||||||||||||
Gas imbalances | 0 | 0 | ||||||||||||||||||||||||||
Number of PGA discretionary changes | 3 | |||||||||||||||||||||||||||
Months between PGA discretionary changes | 2 months | |||||||||||||||||||||||||||
Cost savings retention percentage | 10.00% | |||||||||||||||||||||||||||
Maximum amount of cost savings allowable | 3,000,000.0 | |||||||||||||||||||||||||||
Number of months of the original maturity of debt instruments purchased | 3 months | |||||||||||||||||||||||||||
Gross Receipts taxes recorded in regulated gas distribution operating revenues | 96,900,000 | 40,800,000 | 35,900,000 | 76,300,000 | 20,600,000 | |||||||||||||||||||||||
Finance receivable, net | 10,900,000 | 10,800,000 | ||||||||||||||||||||||||||
Threshold period past due for collection | 90 days | |||||||||||||||||||||||||||
Threshold period past due for write-off of financing receivable | 12 months | |||||||||||||||||||||||||||
Finance receivable 90 days past due | 300,000 | 300,000 | 400,000 | |||||||||||||||||||||||||
Write off on an allowance for credit losses | $ 300,000 | $ 400,000 |