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Pension and Retirement Plans - Components of net periodic benefit costs (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Sep. 30, 2023 | Sep. 30, 2022
Defined Benefit Plan Disclosure [Line Items] |  |
Increase (decrease) in minimum liability included in other comprehensive income (loss) | $ (244) | $ (4,096)
U.K.. |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Increase (decrease) in minimum liability included in other comprehensive income (loss) | (313) | (3,509)
U.S. |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Increase (decrease) in minimum liability included in other comprehensive income (loss) | 69 | (587)
Pension: |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Interest cost | 442 | 279
Expected return on plan assets | (575) | (449)
Amortization of past service costs | 7 | 7
Amortization of net (gain) loss | (4) | 98
Net periodic benefit cost | (130) | (65)
Increase (decrease) in minimum liability included in other comprehensive income (loss) | (314) | (3,529)
Pension: | International |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Interest cost | 429 | 268
Pension: | U.K.. |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Interest cost | 429 | 268
Expected return on plan assets | (575) | (449)
Amortization of past service costs | 7 | 7
Amortization of net (gain) loss | 0 | 97
Net periodic benefit cost | (139) | (77)
Increase (decrease) in minimum liability included in other comprehensive income (loss) | (313) | (3,509)
Pension: | U.S. |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Interest cost | 13 | 11
Expected return on plan assets | 0 | 0
Amortization of past service costs | 0 | 0
Amortization of net (gain) loss | (4) | 1
Net periodic benefit cost | 9 | 12
Increase (decrease) in minimum liability included in other comprehensive income (loss) | (1) | (20)
Post Retirement: |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service cost | 24 | 44
Interest cost | 62 | 46
Amortization of net (gain) loss | (196) | (7)
Net periodic benefit cost | (110) | 83
Increase (decrease) in minimum liability included in other comprehensive income (loss) | 70 | (567)
Post Retirement: | International |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service cost | 0 | 0
Interest cost | 0 | 0
Post Retirement: | U.K.. |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service cost | 0 | 0
Interest cost | 0 | 0
Amortization of net (gain) loss | 0 | 0
Net periodic benefit cost | 0 | 0
Increase (decrease) in minimum liability included in other comprehensive income (loss) | 0 | 0
Post Retirement: | U.S. |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service cost | 24 | 44
Interest cost | 62 | 46
Amortization of net (gain) loss | (196) | (7)
Net periodic benefit cost | (110) | 83
Increase (decrease) in minimum liability included in other comprehensive income (loss) | $ 70 | $ (567)

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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 3A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480535/715-20-45-3A Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-18 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (h)(4) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(4) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-6 + Details
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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 3A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480535/715-20-45-3A Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-18 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (h)(5) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(5) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-6 + Details
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- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 3A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480535/715-20-45-3A Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-18 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (h)(3) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(3) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-6 + Details
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