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Regulatory Matters - Spire - Additional Information (Details) - USD ($) $ in Thousands |  |  |  |  |  | 1 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | --- | ---
Oct. 23, 2020 | Aug. 28, 2020 | Aug. 30, 2019 | Sep. 14, 2018 | Feb. 01, 2018 | Dec. 31, 2015 | Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2018
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Regulatory costs |  |  |  |  |  |  | $ 0 | $ 0 | $ 30,600
Spire Gulf |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Approved return rate on equity | 10.70% |  |  |  |  |  | 10.70% |  |
Rate increase (decrease), margin of index range |  |  |  |  |  |  | 1.50% |  |
Pro-rate rating for equity content |  |  |  |  |  |  | 75.00% |  |
Revenue variances |  |  |  |  |  |  | $ 100 |  |
Single force majeure |  |  |  |  |  |  | 100 |  |
Multiple force majeures |  |  |  |  |  |  | $ 150 |  |
Recovery percentage of incurred costs |  |  |  |  |  |  | 90.00% |  |
Approved point to refund |  |  |  |  |  |  | $ 1,400 |  |
Approved rate increase (decrease) amount |  |  |  |  |  |  | 1,800 |  |
Approved rate increase (decrease), annualized revenue | $ 1,100 |  |  |  |  |  |  |  |
Spire |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Regulatory costs |  |  |  |  | $ 1,900 |  |  |  |
Spire Mississippi |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Approved return rate on equity |  |  |  |  |  |  |  | 9.79% |
Excess of allowed return on equity |  |  |  |  |  |  |  | 1.00% |
Return on equity shortfall |  |  |  |  |  |  |  | 75.00% |
Excess return on equity |  |  |  |  |  |  |  | 50.00% |
Recovery period |  |  |  |  |  | 3 years |  |  |
APSC | Spire |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Line of credit facility borrowing capacity |  |  |  |  |  |  | 50,000 |  |
Principal amount outstanding |  |  |  |  |  |  | $ 25,000 |  |
MoPSC |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Approved rate increase (decrease), annualized revenue |  | $ 600 | $ 300 | $ 700 |  |  |  |  |
Minimum [Member] | Spire Gulf |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Approved return rate on equity |  |  |  |  |  |  | 10.45% |  |
Maximum | Spire Gulf |  |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |  |
Approved return rate on equity |  |  |  |  |  |  | 10.95% |  |

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