Retirement Benefit Plans - Roll Forward of Defined Benefit Pension Plan Obligations and Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Benefit obligations:
Benefit obligations at beginning of year	$ 30,548	$ 27,437
Service cost	341	299
Interest cost	832	1,055
Actuarial loss	2,037	3,691
Benefits paid	(1,965)	(1,914)
Currency translation	0	(20)
Benefit obligations at end of year	31,793	30,548
Plan assets:
Plan assets at beginning of year	20,970	22,052
Actual return on plan assets	1,930	622
Employer contributions	674	210
Benefits paid	(1,965)	(1,914)
Plan assets at end of year	$ 21,609	$ 20,970