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Retirement Benefit Plans - Asset Allocation of Defined Benefit Pension Plan Assets and Fair Values and Levels in Fair Value Hierarchy (Details) - USD ($) $ in Thousands | Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | $ 17,194 | $ 17,937 | $ 23,211
Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 17,194 |  |
Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 16,108 |
Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 1,829 | $ 2,108
Large value |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 879 | 393 |
Large value | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 879 |  |
Large value | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 393 |
Large value | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 0 |
Large blend |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 3,124 | 7,637 |
Large blend | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 3,124 |  |
Large blend | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 7,637 |
Large blend | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 0 |
Large growth |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 1,060 | 302 |
Large growth | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 1,060 |  |
Large growth | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 302 |
Large growth | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 0 |
Mid blend |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 599 | 167 |
Mid blend | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 599 |  |
Mid blend | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 167 |
Mid blend | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 0 |
Small blend |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 499 | 359 |
Small blend | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 499 |  |
Small blend | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 359 |
Small blend | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 0 |
Foreign large blend |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 615 | 1,276 |
Foreign large blend | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 615 |  |
Foreign large blend | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 1,276 |
Foreign large blend | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 0 |
Diversified emerging markets |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 272 | 63 |
Diversified emerging markets | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 272 |  |
Diversified emerging markets | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 63 |
Diversified emerging markets | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 0 |
Global equity securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 577 |  |
Global equity securities | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 577 |  |
Inflation protected bond |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 971 |
Inflation protected bond | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  |  |
Inflation protected bond | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 971 |
Inflation protected bond | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 0 |
Intermediate term bond |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 5,676 | 6,332 |
Intermediate term bond | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 5,676 |  |
Intermediate term bond | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 4,503 |
Intermediate term bond | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 1,829 |
Multi-sector bond |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 2,044 |  |
Multi-sector bond | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 2,044 |  |
High inflation bond |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 78 |
High inflation bond | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 78 |
High inflation bond | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 0 |
Emerging markets bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 0 |
Emerging markets bonds | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 0 |
Emerging markets bonds | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 0 |
Cash or money market |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 1,849 |  |
Cash or money market | Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | $ 1,849 |  |
Short-term bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 359 |
Short-term bonds | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 359 |
Short-term bonds | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | $ 0 |

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