Retirement and Post-Retirement Employee Benefit Plans - Schedule of Net Benefit Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Supplemental Executive Retirement Plans
Components of net periodic postretirement cost:
Service cost	$ 1,067	$ 1,074	$ 869
Interest cost	3,180	4,188	5,127
Recognized actuarial loss	3,560	3,945	2,227
Settlements	9,151	9,180	0
Net periodic pension cost	16,958	18,387	8,223
Defined Benefit Plan
Components of net periodic postretirement cost:
Service cost	17,369	17,551	15,311
Interest cost	16,883	19,028	22,071
Expected return on assets	(27,913)	(28,316)	(28,451)
Amortization of prior service cost	8,686	(231)	(232)
Recognized actuarial loss	(231)	9,025	4,201
Net periodic pension cost	$ 14,794	$ 17,057	$ 12,900