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v3.23.1

Income Taxes (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Mar. 31, 2023 | Mar. 31, 2022 | Mar. 31, 2023 | Mar. 31, 2022 | Sep. 30, 2022
Income Tax Contingency [Line Items] |  |  |  |  |
Effective income tax rate | 11.20% | 10.10% | 11.10% | 8.30% |
Regulatory liabilities | $ 1,355,310 |  | $ 1,355,310 |  | $ 1,358,907
Regulatory excess deferred taxes |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |
Deferred tax liabilities, net | 418,900 |  | 418,900 |  |
Regulatory liabilities | 466,496 |  | 466,496 |  | 545,021
Regulatory excess deferred taxes | Other Current Liabilities |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |
Deferred tax liabilities, net | 151,400 |  | 151,400 |  | $ 159,800
Regulatory excess deferred taxes, to be returned, tranche one |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |
Deferred tax liabilities, net | 332,200 |  | $ 332,200 |  |
Regulatory excess deferred taxes, to be returned, tranche one | Minimum |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |
Return basis, term |  |  | 35 months |  |
Regulatory excess deferred taxes, to be returned, tranche one | Maximum |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |
Return basis, term |  |  | 60 months |  |
Regulatory excess deferred taxes, to be returned, tranche two |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |
Regulatory liabilities | 71,600 |  | $ 71,600 |  |
Regulatory excess deferred taxes, to be returned, tranche two | Minimum |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |
Return basis, term |  |  | 15 years |  |
Regulatory excess deferred taxes, to be returned, tranche two | Maximum |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |
Return basis, term |  |  | 69 years |  |
Regulatory excess deferred taxes, to be returned, tranche three |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |
Deferred tax liabilities, net | $ 15,100 |  | $ 15,100 |  |

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