Retirement Benefit Plans - Roll Forward of Defined Benefit Pension Plan Obligations and Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Benefit obligations:
Benefit obligations at beginning of year	$ 29,731	$ 27,685
Service cost	324	280
Interest cost	883	1,017
Actuarial (loss) gain	(1,292)	2,405
Benefits paid	(1,740)	(1,659)
Currency translation	15	3
Plan assets at end of year	27,921	29,731
Plan assets:
Plan assets at beginning of year	21,344	20,896
Actual return on plan assets	1,978	2,061
Employer contributions	109	46
Benefits paid	(1,740)	(1,659)
Plan assets at end of year	$ 21,691	$ 21,344