Pension and Post-retirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Pension Plans
Pension Plan and Retirement Benefits
Service cost	$ 1,310	$ 1,384	$ 2,620	$ 2,768
Interest cost	2,567	2,625	5,133	5,231
Expected return	(3,575)	(3,665)	(7,147)	(7,299)
Amortizations	401	1,294	803	2,583
Net periodic benefit cost	703	1,638	1,409	3,283
Postretirement Health Care Benefits
Pension Plan and Retirement Benefits
Service cost	79	84	158	168
Interest cost	1,088	1,078	2,176	2,156
Amortizations	372	751	744	1,500
Net periodic benefit cost	1,539	$ 1,913	3,078	$ 3,824
Contribution to plan			1,666
Expected future employer contribution	3,334		3,334
U.S. pension plan | Defined Benefit Pension Plans
Pension Plan and Retirement Benefits
Contribution to plan			1,500
Expected future employer contribution	3,000		3,000
U.K. pension plan | Defined Benefit Pension Plans
Pension Plan and Retirement Benefits
Contribution to plan			391
Expected future employer contribution	$ 391		$ 391