Pension Plan and Retirement Benefits - Defined Benefit Plans - Recognized in BS (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Accrued pension and postretirement benefits:
Current	$ (5,095)	$ (5,095)
Non-current	(159,641)	(199,815)
Accrued pension and postretirement benefits	(164,736)	(204,910)
Accumulated other comprehensive loss:
Net (gain) loss	60,699	102,105
Prior service cost	1,839	2,213
Total accumulated other comprehensive loss	62,538	104,318
Amounts expected to be recognized from AOCI into the statement of operations in the following year:
Amortization of net loss	2,951	7,909
Amortization of prior service cost	205	374
Total	3,156	8,283
Accumulated benefit obligation	269,386	299,197
Defined Benefit Pension Plans
Accrued pension and postretirement benefits:
Non-current	(56,007)	(86,709)
Accrued pension and postretirement benefits	(56,007)	(86,709)
Accumulated other comprehensive loss:
Net (gain) loss	38,808	66,819
Prior service cost	1,839	2,213
Total accumulated other comprehensive loss	40,647	69,032
Amounts expected to be recognized from AOCI into the statement of operations in the following year:
Amortization of net loss	1,464	4,910
Amortization of prior service cost	205	374
Total	1,669	5,284
Defined Benefit Pension Plans | Other assets
Accrued pension and postretirement benefits:
Noncurrent assets	5,444	3,566
Non-current	(61,451)	(90,275)
Postretirement Health Care Benefits
Accrued pension and postretirement benefits:
Current	(5,000)	(5,000)
Non-current	(103,013)	(112,424)
Accrued pension and postretirement benefits	(108,013)	(117,424)
Accumulated other comprehensive loss:
Net (gain) loss	21,891	35,286
Total accumulated other comprehensive loss	21,891	35,286
Amounts expected to be recognized from AOCI into the statement of operations in the following year:
Amortization of net loss	1,487	2,999
Total	1,487	2,999
Non-qualified pension plan
Accrued pension and postretirement benefits:
Current	(95)	(95)
Non-current	(621)	(682)
Accrued pension and postretirement benefits	$ (716)	$ (777)