Pension Plan and Retirement Benefits - Defined Benefit Plans - Recognized in BS (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Accrued pension and postretirement benefits:
Current	$ (2,940)	$ (3,371)
Non-current	(54,697)	(74,150)
Accrued pension and postretirement benefits	(57,637)	(77,521)
Accumulated other comprehensive (income) loss:
Net (income) loss	22,036	8,311
Prior service cost	1,130	1,365
Total accumulated other comprehensive (income) loss	(20,906)	(6,946)
Accumulated benefit obligation	216,287	227,915
Defined Benefit Pension Plan
Accrued pension and postretirement benefits:
Non-current	(4,819)	(12,954)
Accrued pension and postretirement benefits	(4,819)	(12,954)
Accumulated other comprehensive (income) loss:
Net (income) loss	(20,663)	(22,496)
Prior service cost	1,130	1,365
Total accumulated other comprehensive (income) loss	21,793	23,861
Defined Benefit Pension Plan | Other assets
Accrued pension and postretirement benefits:
Noncurrent assets	8,803	7,702
Non-current	(13,622)	(20,655)
Defined Benefit Other Postretirement Benefit Plan
Accrued pension and postretirement benefits:
Current	(2,845)	(3,276)
Non-current	(49,481)	(60,761)
Accrued pension and postretirement benefits	(52,326)	(64,037)
Accumulated other comprehensive (income) loss:
Net (income) loss	42,699	30,807
Total accumulated other comprehensive (income) loss	(42,699)	(30,807)
Non Qualified Pension Plans Defined Benefit [Member]
Accrued pension and postretirement benefits:
Current	(95)	(95)
Non-current	(397)	(435)
Accrued pension and postretirement benefits	$ (492)	$ (530)