Pension Plan and Retirement Benefits - Cost Assumptions (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Postretirement Health Care Benefits
Assumptions used to determine net periodic benefit cost
Discount rate (as a percent)	4.25%	4.25%	4.75%
Actuarial losses (gains)	$ 15,283	$ 5,097
Defined Benefit Pension Plans
Assumptions used to determine net periodic benefit cost
Actuarial losses (gains)	$ 32,370	$ 21,861
U.S. pension plan
Assumptions used to determine net periodic benefit cost
Discount rate (as a percent)	4.00%	4.00%	4.50%
Expected return on plan assets (as a percent)	7.50%	7.50%	7.50%
Rate of compensation increase (as a percent)	3.50%	3.50%	3.50%
U.K. pension plan
Assumptions used to determine net periodic benefit cost
Discount rate (as a percent)	3.70%	3.90%	4.30%
Expected return on plan assets (as a percent)	4.10%	4.40%	4.80%