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INCOME TAXES - Narrative (Details) - USD ($) | Sep. 30, 2017 | Sep. 30, 2016
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Tax Credit Carryforward [Line Items] |  |
Federal and state loss carryforwards | $ 478,600,000 |
Contribution carryforwards | 12,100,000 |
Valuation allowance | 500,000 | $ 900,000
Tax credit carryforwards | 2,500,000 |
Unrecognized tax benefits affect on the Company's effective tax rate | 5,100,000 | 3,300,000
Income taxes accrued | 0 | 0
income tax penalties accrued | 0 |
Spire Missouri |  |
Tax Credit Carryforward [Line Items] |  |
Federal and state loss carryforwards | 166,000,000 |
Contribution carryforwards | 11,200,000 |
Valuation allowance | 500,000 | 900,000
Tax credit carryforwards | 2,000,000 |
Unrecognized tax benefits affect on the Company's effective tax rate | 4,800,000 | 3,100,000
Income taxes accrued | 0 | 0
income tax penalties accrued | 0 | $ 0
Spire Alabama |  |
Tax Credit Carryforward [Line Items] |  |
Federal and state loss carryforwards | $ 233,500,000 |

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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible charitable contribution carryforwards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 25 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=96869850&loc=d3e28680-109314 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32632-109319 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32621-109319 + Details
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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
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- Definition Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319 + Details
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- Definition Amount of statutory penalties accrued for a tax position claimed or expected to be claimed by the entity, in its tax return. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319 + Details
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