Retirement Benefit Plans - Narrative (Details)	12 Months Ended
	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