Pension Plan and Retirement Benefits - Defined Benefit Plans - Expense (Details) $ in Thousands		1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 01, 2007 USD ($)	Mar. 31, 2006 USD ($)	Sep. 30, 2016 USD ($) person	Sep. 30, 2016 USD ($) person	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)
Pension Plan and Retirement Benefits
Accrued pension and postretirement benefits			$ 255,346	$ 255,346	$ 217,837
Defined Benefit Pension Plans
Pension Plan and Retirement Benefits
Pension plan expense				11,396	5,437	$ 6,347
Accrued pension and postretirement benefits			$ 129,375	129,375	106,445
Contribution to plan				6,778	2,409
U.S. pension plan
Pension Plan and Retirement Benefits
Contribution to plan				$ 6,000	1,500
Number of participants that received distribution | person			146	146
Amount of distributions			$ 8,688,000
U.K. pension plan
Pension Plan and Retirement Benefits
Contribution to plan				$ 778	909
Non-qualified pension plan
Pension Plan and Retirement Benefits
Pension plan expense				91	140	84
Accrued pension and postretirement benefits			854	854	858
Postretirement Health Care Benefits
Pension Plan and Retirement Benefits
Pension plan expense				7,652	7,155	$ 3,946
Accrued pension and postretirement benefits			$ 125,117	125,117	110,534
Maximum liability related to total retiree health care costs under plan amendment	$ 5,000
Reduction in accumulated postretirement benefit liability due to plan amendment		$ 46,313
Period of amortization as a reduction to expense		8 years
Contribution to plan				$ 5,527	$ 4,672