Retirement Benefit Plans - Roll Forward of Defined Benefit Pension Plan Obligations and Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Benefit obligations:
Benefit obligations at beginning of year	$ 22,795	$ 29,330
Service cost	24	42
Interest cost	1,090	714
Actuarial (gain)	(1,463)	(5,265)
Benefits paid	(1,814)	(1,970)
Currency translation	25	(56)
Benefit obligations at end of year	20,657	22,795
Plan assets:
Plan assets at beginning of year	17,937	23,211
Actual return on plan assets	979	(3,376)
Employer contributions	92	72
Benefits paid	(1,814)	(1,970)
Plan assets at end of year	17,194	17,937
Underfunded status at end of year	$ (3,463)	$ (4,858)