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Retirement Benefit Plans - Narrative (Details) | 12 Months Ended |
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Sep. 30, 2020 USD ($) plan | Sep. 30, 2019 USD ($) | Jan. 01, 2020 USD ($)
Defined Benefit Plan Disclosure [Line Items] |  |  |
Number of defined benefit pension plans | plan | 4 |  |
Employer contributions | $ 245,000 |  |
Plan funded percentage | 89.00% |  |
Other debt withdrawal liability | $ 739,000 |  |
Employer matching contribution percentage of employees' gross pay | 100.00% |  |
Percentage of eligible compensation of deferral contribution, minimum | 1.00% |  |
Percentage of eligible compensation | 80.00% |  |
Percentage of eligible compensation of deferral contribution, maximum | 6.00% |  |
Matching contribution expense for defined contribution plan | $ 648,000 | $ 470,000 |
Non-elective contribution per hour |  |  | $ 1.50
Non-elective contribution expense | $ 56,000 |  |
IAM National Pension Fund |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Payment period | 20 years |  |

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- Definition Percentage of deferral participant contribution. + References No definition available. + Details
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- Definition Percentage of eligible compensation of deferral contribution minimum. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Amount of contribution expected to be received by defined benefit plan from employer in next fiscal year following current fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4587-114921 + Details
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- Details
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