Pension and Post-retirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Defined Benefit Pension Plans
Pension Plan and Retirement Benefits
Service cost	$ 1,386	$ 1,309	$ 4,159	$ 3,929
Interest cost	2,148	2,567	6,444	7,700
Expected return	(3,639)	(3,561)	(10,907)	(10,708)
Amortizations	1,860	402	5,578	1,205
Net periodic benefit cost	1,755	717	5,274	2,126
Postretirement Health Care Benefits
Pension Plan and Retirement Benefits
Service cost	354	79	1,062	237
Interest cost	874	1,088	2,620	3,264
Amortizations	462	372	1,386	1,116
Net periodic benefit cost	1,690	$ 1,539	5,068	$ 4,617
Contribution to plan			2,141
Expected future employer contribution	2,013		2,013
U.S. pension plan | Defined Benefit Pension Plans
Pension Plan and Retirement Benefits
Contribution to plan			4,500
Expected future employer contribution	1,500		1,500
U.K. pension plan | Defined Benefit Pension Plans
Pension Plan and Retirement Benefits
Contribution to plan			491
Expected future employer contribution	$ 0		$ 0