Retirement Benefit Plans - Changes in the Fair Value of Level 3 Defined Benefit Plan Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Changes in the fair value of the Company's Level 3 investments
Plan assets at beginning of year	$ 21,609	$ 20,970
Actual return on plan assets	3,825	1,930
Plan assets at end of year	23,211	21,609
Level 3
Changes in the fair value of the Company's Level 3 investments
Plan assets at beginning of year	2,098	2,005
Actual return on plan assets	52	128
Purchases and sales of plan assets, net	(42)	(35)
Plan assets at end of year	$ 2,108	$ 2,098