Retirement Benefit Plans - Net Pension Expense for Defined Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Retirement Benefits [Abstract]
Service cost	$ 131	$ 341
Interest cost	699	832
Expected return on plan assets	(1,421)	(1,453)
Amortization of net loss	846	752
Settlement cost	274	239
Net pension expense for defined benefit plans	$ 529	$ 711