Retirement Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Retirement Benefits [Abstract]
Service cost	$ 63	$ 78	$ 189	$ 235
Interest cost	240	221	719	662
Expected return on plan assets	(402)	(404)	(1,205)	(1,211)
Amortization of net loss	161	215	483	646
Net periodic cost	$ 62	$ 110	$ 186	$ 332