Retirement Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Retirement Benefits [Abstract]
Service cost	$ 26	$ 85	$ 78	$ 255
Interest cost	175	208	525	624
Expected return on plan assets	(355)	(363)	(1,066)	(1,090)
Amortization of net loss	211	188	634	564
Net periodic cost	$ 57	$ 118	$ 171	$ 353