Pension Plan and Retirement Benefits - Defined Benefit Plans - Recognized in BS (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Accrued pension and postretirement benefits:
Current	$ (5,095)	$ (5,095)
Non-current	(199,815)	(250,251)
Accrued pension and postretirement benefits	(204,910)	(255,346)
Accumulated other comprehensive loss:
Net (gain) loss	102,105	164,024
Prior service cost	2,213	3,020
Total accumulated other comprehensive loss	104,318	167,044
Amounts expected to be recognized from AOCI into the statement of operations in the following year:
Amortization of net loss	7,909	15,546
Amortization of prior service cost	374	808
Total	8,283	16,354
Accumulated benefit obligation	299,197	317,754
Defined Benefit Pension Plans
Accrued pension and postretirement benefits:
Non-current	(86,709)	(129,375)
Accrued pension and postretirement benefits	(86,709)	(129,375)
Accumulated other comprehensive loss:
Net (gain) loss	66,819	116,388
Prior service cost	2,213	3,020
Total accumulated other comprehensive loss	69,032	119,408
Amounts expected to be recognized from AOCI into the statement of operations in the following year:
Amortization of net loss	4,910	11,268
Amortization of prior service cost	374	808
Total	5,284	12,076
U.S. pension plan | Accrued pension benefits
Accrued pension and postretirement benefits:
Non-current	(90,275)
U.K. pension plan | Other assets | U.K. subsidiary
Accrued pension and postretirement benefits:
Noncurrent assets	3,566
Postretirement Health Care Benefits
Accrued pension and postretirement benefits:
Current	(5,000)	(5,000)
Non-current	(112,424)	(120,117)
Accrued pension and postretirement benefits	(117,424)	(125,117)
Accumulated other comprehensive loss:
Net (gain) loss	35,286	47,636
Total accumulated other comprehensive loss	35,286	47,636
Amounts expected to be recognized from AOCI into the statement of operations in the following year:
Amortization of net loss	2,999	4,278
Total	2,999	4,278
Non-qualified pension plan
Accrued pension and postretirement benefits:
Current	(95)	(95)
Non-current	(682)	(759)
Accrued pension and postretirement benefits	$ (777)	$ (854)