Retirement Benefit Plans - Roll Forward of Defined Benefit Pension Plan Obligations and Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Benefit obligations:
Benefit obligations at beginning of year	$ 31,793	$ 30,548
Service cost	131	341
Interest cost	699	832
Actuarial (gain) loss	(967)	2,037
Benefits paid	(2,349)	(1,965)
Currency translation	23	0
Benefit obligations at end of year	29,330	31,793
Plan assets:
Plan assets at beginning of year	21,609	20,970
Actual return on plan assets	3,825	1,930
Employer contributions	126	674
Benefits paid	(2,349)	(1,965)
Plan assets at end of year	23,211	$ 21,609
Decrease in benefit obligation	$ (2,463)