Retirement Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Retirement Benefits [Abstract]
Service cost	$ 26	$ 85
Interest cost	175	208
Expected return on plan assets	(355)	(376)
Amortization of net loss	211	188
Net periodic cost	$ 57	$ 105