SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Millions	6 Months Ended	12 Months Ended
Mar. 31, 2016 USD ($) reporting_unit	Mar. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)
Related Party Transaction [Line Items]
Number of operating segments \| reporting_unit	2
Finance receivables, net	$ 11.1	$ 10.7	$ 11.2
Laclede Gas
Related Party Transaction [Line Items]
Accrued unbilled revenues	57.4	63.5	27.6
Accruals for capital expenditures	5.3	4.2	9.6
Alagasco
Related Party Transaction [Line Items]
Accrued unbilled revenues	14.9	15.0	6.4
Accruals for capital expenditures	$ 3.7	4.7	3.1
Threshold period past due for collection	90 days
Threshold period past due for write-off of financing receivable	12 months
Write-off on an allowance for credit losses	$ 0.4	0.3	0.4
Alagasco \| Financing Receivables, Equal to Greater than 90 Days Past Due
Related Party Transaction [Line Items]
Financing receivable 90 days past due	$ 0.4	$ 0.3	$ 0.4

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- Definition

For an unclassified balance sheet, the amount of fees and other revenue, excluding investment income receivable, earned but not yet received, which were recognized in conformity with revenue recognition criteria based on estimates or specific contractual terms.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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- Definition

Future cash outflow to pay for purchases of fixed assets that have occurred.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586

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-Name Accounting Standards Codification
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- Definition

Amount of direct write-downs of financing receivables charged against the allowance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
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- Definition

Recorded Investment in financing receivables that are past due at the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

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Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Threshold period past due for financing receivable to write off as uncollectible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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