Pension and Post-retirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Defined Benefit Pension Plans
Pension Plan and Retirement Benefits
Service cost	$ 1,570	$ 1,020	$ 3,141	$ 2,040
Interest cost	2,592	2,865	5,141	5,713
Expected return	(3,531)	(3,399)	(7,003)	(6,775)
Amortizations	2,994	2,385	5,975	4,766
Net periodic cost	3,625	2,871	7,254	5,744
U.S. pension plan
Pension Plan and Retirement Benefits
Contribution to plan			3,000
Expected future employer contribution			3,000
U.K. pension plan
Pension Plan and Retirement Benefits
Contribution to plan			373
Expected future employer contribution			405
Postretirement Health Care Benefits
Pension Plan and Retirement Benefits
Service cost	87	58	174	116
Interest cost	1,073	1,149	2,146	2,298
Amortizations	1,070	706	2,140	1,412
Net periodic cost	$ 2,230	$ 1,913	4,460	$ 3,826
Contribution to plan			2,612
Expected future employer contribution			$ 2,388