Retirement and Post-Retirement Employee Benefit Plans - Schedule of Net Benefit Costs Postretirement (Details) - Postretirement Plans - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Components of net periodic postretirement cost:
Service cost	$ 11,000	$ 13,466	$ 10,810
Interest cost	15,372	10,612	11,839
Expected return on assets	(10,455)	(10,499)	(10,659)
Amortization of transition obligation	0	0	0
Amortization of prior service cost	30,533	173	173
Recognized actuarial loss	1,172	(1,337)	(8,178)
Net periodic pension cost	$ 47,622	$ 12,415	$ 3,985