COMMITMENTS AND CONTINGENCIES - Commitments (Details) MMcf in Thousands, $ in Millions	12 Months Ended
Sep. 30, 2016 USD ($) MMcf
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	$ 1,647.8
Laclede Gas
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	1,227.6
Laclede Gas \| Purchase Commitment \| Subsidiary of Common Parent
Long-term Purchase Commitment [Line Items]
Annual purchase commitment	$ 1.0
Commitment termination minimum required notification period	6 months
Alagasco
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	$ 352.7
Alagasco \| Inventories
Long-term Purchase Commitment [Line Items]
Minimum volume purchase commitment required (in Mmcf) \| MMcf	93

Purchase Commitment, Termination, Minimum Notification Period Required

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- Definition

The minimum amount the entity agreed to spend under the long-term purchase commitment.

+ References

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Volume that must be purchased within the specified time period of the agreement to avoid penalties or unfavorable effects on pricing, among other adverse consequences.

+ References

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- Definition

Minimum amount to be expended to satisfy the terms of arrangements in which the entity has agreed to expend funds to procure goods or services, excluding long-term purchase commitments or unconditional purchase obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(19))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(17))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(25))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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