Pension Plan and Retirement Benefits - Defined Benefit Plans - Recognized in BS (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Accrued pension and postretirement benefits:
Current	$ (4,250)	$ (5,095)
Non-current	(205,864)	(159,641)
Accrued pension and postretirement benefits	(210,114)	(164,736)
Accumulated other comprehensive loss:
Net (gain) loss	105,361	60,699
Prior service cost	2,066	1,839
Total accumulated other comprehensive loss	107,427	62,538
Accumulated benefit obligation	309,410	269,386
Defined Benefit Pension Plans
Accrued pension and postretirement benefits:
Non-current	(95,561)	(56,007)
Accrued pension and postretirement benefits	(95,561)	(56,007)
Accumulated other comprehensive loss:
Net (gain) loss	80,711	38,808
Prior service cost	2,066	1,839
Total accumulated other comprehensive loss	82,777	40,647
Defined Benefit Pension Plans | Other assets
Accrued pension and postretirement benefits:
Noncurrent assets	5,627	5,444
Non-current	(101,188)	(61,451)
Postretirement Health Care Benefits
Accrued pension and postretirement benefits:
Current	(4,155)	(5,000)
Non-current	(109,679)	(103,013)
Accrued pension and postretirement benefits	(113,834)	(108,013)
Accumulated other comprehensive loss:
Net (gain) loss	24,650	21,891
Total accumulated other comprehensive loss	24,650	21,891
Non-qualified pension plan
Accrued pension and postretirement benefits:
Current	(95)	(95)
Non-current	(624)	(621)
Accrued pension and postretirement benefits	$ (719)	$ (716)