Pension and Post-retirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Pension Plans
Pension Plan and Retirement Benefits
Service cost	$ 1,387	$ 1,310	$ 2,773	$ 2,620
Interest cost	2,148	2,567	4,296	5,133
Expected return	(3,623)	(3,575)	(7,268)	(7,147)
Amortizations	1,859	401	3,718	803
Net periodic benefit cost	1,771	703	3,519	1,409
Postretirement Health Care Benefits
Pension Plan and Retirement Benefits
Service cost	354	79	708	158
Interest cost	873	1,088	1,746	2,176
Amortizations	462	372	924	744
Net periodic benefit cost	1,689	$ 1,539	3,378	$ 3,078
Contribution to plan			1,424
Expected future employer contribution	2,730		2,730
U.S. pension plan | Defined Benefit Pension Plans
Pension Plan and Retirement Benefits
Contribution to plan			3,000
Expected future employer contribution	3,000		3,000
U.K. pension plan | Defined Benefit Pension Plans
Pension Plan and Retirement Benefits
Contribution to plan			370
Expected future employer contribution	$ 368		$ 368