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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, 2019 | Sep. 30, 2018 | Sep. 30, 2017
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | $ 20,970 | $ 22,052 | $ 21,691
Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 18,965 | 20,237 |
Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 2,005 | 1,815 | $ 2,175
Large value |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 435 | 446 |
Large value | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 435 | 446 |
Large value | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Large blend |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 9,368 | 9,910 |
Large blend | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 9,368 | 9,910 |
Large blend | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Large growth |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 625 | 825 |
Large growth | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 625 | 825 |
Large growth | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Mid blend |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 163 | 228 |
Mid blend | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 163 | 228 |
Mid blend | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Small blend |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 159 | 229 |
Small blend | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 159 | 229 |
Small blend | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Foreign large blend |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 1,607 | 1,714 |
Foreign large blend | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 1,607 | 1,714 |
Foreign large blend | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Diversified emerging markets |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 17 | 18 |
Diversified emerging markets | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 17 | 18 |
Diversified emerging markets | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Inflation protected bond |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 1,100 | 1,184 |
Inflation protected bond | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 1,100 | 1,184 |
Inflation protected bond | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Intermediate term bond |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 6,974 | 6,811 |
Intermediate term bond | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 4,969 | 4,996 |
Intermediate term bond | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 2,005 | 1,815 |
High inflation bond |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 173 | 182 |
High inflation bond | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 173 | 182 |
High inflation bond | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Emerging markets bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 106 | 38 |
Emerging markets bonds | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 106 | 38 |
Emerging markets bonds | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Short-term bonds |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 243 | 467 |
Short-term bonds | Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 243 | 467 |
Short-term bonds | Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | $ 0 | $ 0 |

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