Retirement Benefit Plans - Net Pension Expense for Defined Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Retirement Benefits [Abstract]
Service cost	$ 341	$ 299
Interest cost	832	1,055
Expected return on plan assets	(1,453)	(1,573)
Amortization of net loss	752	429
Settlement cost	239	246
Net pension expense for defined benefit plans	$ 711	$ 456