Retirement Benefit Plans - Net Pension Expense for Defined Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Components of net periodic benefit cost
Service cost	$ 299	$ 262
Interest cost	1,055	963
Expected return on plan assets	(1,573)	(1,608)
Amortization of net loss	429	641
Settlement cost	246	0
Net pension expense for defined benefit plans	$ 456	$ 258