Retirement Benefit Plans - Roll Forward of Defined Benefit Pension Plan Obligations and Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Benefit obligations:
Benefit obligations at beginning of year	$ 27,921	$ 29,731
Service cost	262	324
Interest cost	963	883
Actuarial (loss) gain	178	(1,292)
Benefits paid	(1,880)	(1,740)
Currency translation	(7)	15
Benefit obligations at end of year	27,437	27,921
Plan assets:
Plan assets at beginning of year	21,691	21,344
Actual return on plan assets	2,118	1,978
Employer contributions	123	109
Benefits paid	(1,880)	(1,740)
Plan assets at end of year	$ 22,052	$ 21,691