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v3.25.1

Income Taxes (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Mar. 31, 2025 | Mar. 31, 2024 | Mar. 31, 2025 | Mar. 31, 2024 | Sep. 30, 2024
Income Tax Contingency [Line Items] |  |  |  |  |
Effective income tax rate | 19.50% | 15.70% | 19.00% | 15.30% |
Regulatory liabilities | $ 1,275,303 |  | $ 1,275,303 |  | $ 1,227,882
Regulatory excess deferred taxes |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |
Deferred tax liabilities, net | 178,600 |  | 178,600 |  |
Regulatory liabilities | 229,096 |  | 229,096 |  | 257,001
Regulatory excess deferred taxes | Other Current Liabilities |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |
Deferred tax liabilities, net | 73,900 |  | 73,900 |  | $ 79,700
Regulatory excess deferred taxes, to be returned, tranche one |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |
Deferred tax liabilities, net | 115,500 |  | $ 115,500 |  |
Regulatory excess deferred taxes, to be returned, tranche one | Minimum |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |
Return basis, term |  |  | 12 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 | 48,600 |  | $ 48,600 |  |
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 |  |  | 68 years |  |
Regulatory excess deferred taxes, to be returned, tranche three |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |
Deferred tax liabilities, net | $ 14,500 |  | $ 14,500 |  |

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