Retirement and Postretirement Employee Benefit Plans - Supplemental Plans’ Accumulated Benefit Obligation, Projected Benefit Obligation and Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Reconciliation:
Net amount recognized	$ 29,498	$ 0
Supplemental Executive Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	79,233	100,981
Change in projected benefit obligation:
Benefit obligation at beginning of year	104,301	129,140
Service cost	1,129	1,067	$ 1,074
Interest cost	2,647	3,180	4,188
Actuarial (gain) loss	(22,471)	1,332
Benefits paid	(4,831)	(4,720)
Settlements	0	(25,698)
Benefit obligation at end of year	80,775	104,301	129,140
Change in plan assets:
Fair value of plan assets at beginning of year	0	0
Employer contribution	4,831	30,418
Benefits paid	(4,831)	(4,720)
Settlements	0	(25,698)
Fair value of plan assets at end of year	0	0	$ 0
Reconciliation:
Funded status	(80,775)	(104,301)
Unrecognized prior service cost	0	0
Unrecognized net loss	0	0
Net amount recognized	$ (80,775)	$ (104,301)