Retirement Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Retirement Benefits [Abstract]
Service cost	$ 85	$ 74	$ 255	$ 224
Interest cost	208	264	624	791
Expected return on plan assets	(363)	(393)	(1,090)	(1,180)
Amortization of net loss	188	107	564	322
Net periodic cost	$ 118	$ 52	$ 353	$ 157