Retirement Benefit Plans - Net Pension Expense for Defined Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Components of net periodic benefit cost
Service cost	$ 324	$ 280
Interest cost	883	1,017
Pension Plan | United States
Components of net periodic benefit cost
Service cost	324	280
Interest cost	883	1,017
Expected return on plan assets	(1,615)	(1,632)
Amortization of net loss	861	828
Settlement cost	0	223
Net pension expense for defined benefit plan	$ 453	$ 716