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Retirement and Postretirement Employee Benefit Plans - Schedule of Employee Pension Plans Investments at Fair Value (Details) - Employee Pension Plan - USD ($) $ in Thousands | Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023
--- | --- | --- | ---
Derivatives, Fair Value [Line Items] |  |  |
Total investments | $ 624,503 | $ 595,212 | $ 502,412
Fair Value, Recurring |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 619,429 | 594,491 |
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 499,028 | 459,723 |
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Common stocks |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 284,573 | 289,301 |
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Money market funds |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 16,293 | 14,542 |
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Registered investment companies |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 123,022 | 90,086 |
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Mortgage-backed securities |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 26,101 | 24,383 |
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | U.S. treasuries |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 15,047 | 9,425 |
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Corporate bonds |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 32,517 | 31,986 |
Fair Value, Recurring | Fair Value, Inputs, Level 1, 2 and 3 | Asset-backed securities |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 1,475 |  |
Fair Value, Recurring | Level 1 |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 422,616 | 388,785 |
Fair Value, Recurring | Level 1 | Common stocks |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 284,573 | 289,301 |
Fair Value, Recurring | Level 1 | Money market funds |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 0 | 0 |
Fair Value, Recurring | Level 1 | Registered investment companies |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 123,022 | 90,086 |
Fair Value, Recurring | Level 1 | Mortgage-backed securities |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 0 | 0 |
Fair Value, Recurring | Level 1 | U.S. treasuries |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 15,021 | 9,398 |
Fair Value, Recurring | Level 1 | Corporate bonds |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 0 | 0 |
Fair Value, Recurring | Level 1 | Asset-backed securities |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 0 |  |
Fair Value, Recurring | Level 2 |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 76,412 | 70,938 |
Fair Value, Recurring | Level 2 | Common stocks |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 0 | 0 |
Fair Value, Recurring | Level 2 | Money market funds |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 16,293 | 14,542 |
Fair Value, Recurring | Level 2 | Registered investment companies |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 0 | 0 |
Fair Value, Recurring | Level 2 | Mortgage-backed securities |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 26,101 | 24,383 |
Fair Value, Recurring | Level 2 | U.S. treasuries |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 26 | 27 |
Fair Value, Recurring | Level 2 | Corporate bonds |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 32,517 | 31,986 |
Fair Value, Recurring | Level 2 | Asset-backed securities |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 1,475 |  |
Fair Value, Recurring | Level 3 |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 0 | 0 |
Fair Value, Recurring | Level 3 | Common stocks |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 0 | 0 |
Fair Value, Recurring | Level 3 | Money market funds |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 0 | 0 |
Fair Value, Recurring | Level 3 | Registered investment companies |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 0 | 0 |
Fair Value, Recurring | Level 3 | Mortgage-backed securities |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 0 | 0 |
Fair Value, Recurring | Level 3 | U.S. treasuries |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 0 | 0 |
Fair Value, Recurring | Level 3 | Corporate bonds |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 0 | 0 |
Fair Value, Recurring | Level 3 | Asset-backed securities |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 0 |  |
Fair Value, Recurring | Fair Value Measured at Net Asset Value Per Share | Common/collective trusts |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | 95,558 | 111,103 |
Fair Value, Recurring | Fair Value Measured at Net Asset Value Per Share | Limited partnerships |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Total investments | $ 24,843 | $ 23,665 |

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