Pension and Post-retirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Defined Benefit Pension Plans
Pension Plan and Retirement Benefits
Service cost	$ 1,407	$ 1,387	$ 2,814	$ 2,773
Interest cost	1,808	2,148	3,616	4,296
Expected return	(3,978)	(3,623)	(7,956)	(7,268)
Amortizations	1,956	1,859	3,912	3,718
Net periodic benefit cost	1,193	1,771	2,386	3,519
Contribution to plan			3,000
Expected future employer contribution	3,000		3,000
Postretirement Health Care Benefits
Pension Plan and Retirement Benefits
Service cost	274	354	548	708
Interest cost	573	873	1,146	1,746
Amortizations		462		924
Net periodic benefit cost	847	$ 1,689	1,694	$ 3,378
Contribution to plan			1,400
Expected future employer contribution	$ 1,907		$ 1,907