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Retirement Benefit Plans - Narrative (Details) | 12 Months Ended |  |
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Sep. 30, 2021 USD ($) plan | Sep. 30, 2020 USD ($) | Jan. 01, 2020 USD ($) | Sep. 30, 2019 USD ($)
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Number of defined benefit pension plans | plan | 4 |  |  |
Decrease in benefit obligation | $ 2,463,000 |  |  |
Benefit obligation | 29,330,000 | $ 31,793,000 |  | $ 30,548,000
Employer contributions | $ 83,000 |  |  |
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 | $ 571,000 | 648,000 |  |
Non-elective contribution per hour |  |  | $ 1.50 |
Non-elective contribution expense | $ 112,000 | $ 56,000 |  |
IAM National Pension Fund |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Payment period |  | 20 years |  |

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- Definition Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. + 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 (a) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 + Details
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