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Income Taxes - Narrative (Details) - USD ($) | Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023
--- | --- | --- | ---
Income Taxes [Line Items] |  |  |
Taxes refundable to customers | $ 306,335,000 | $ 305,645,000 |
Recoverable future taxes | 89,247,000 | 80,084,000 |
Unrecognized tax benefits | 0 | 0 | $ 0
Deferred Income Taxes |  |  |
Income Taxes [Line Items] |  |  |
Taxes refundable to customers | 306,300,000 | 305,600,000 |
Recoverable future taxes | $ 89,200,000 | $ 80,100,000 |

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