Retirement Benefit Plans - Roll Forward of Defined Benefit Pension Plan Obligations and Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Benefit obligations:
Benefit obligations at beginning of year	$ 27,437	$ 27,921
Service cost	299	262
Interest cost	1,055	963
Actuarial loss (gain)	3,691	178
Benefits paid	(1,914)	(1,880)
Currency translation	(20)	(7)
Benefit obligations at end of year	30,548	27,437
Plan assets:
Plan assets at beginning of year	22,052	21,691
Actual return on plan assets	622	2,118
Employer contributions	210	123
Benefits paid	(1,914)	(1,880)
Plan assets at end of year	$ 20,970	$ 22,052