Retirement and Postretirement Employee Benefit Plans - 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
Employee Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	428,629	558,639
Change in projected benefit obligation:
Benefit obligation at beginning of year	596,029	604,221
Service cost	16,165	17,369	$ 17,551
Interest cost	17,606	16,883	19,028
Actuarial gain	(141,567)	(7,561)
Benefits paid	(38,706)	(34,883)
Benefit obligation at end of year	449,527	596,029	604,221
Change in plan assets:
Fair value of plan assets at beginning of year	596,806	528,881
Actual return on plan assets	(87,575)	92,808
Employer contribution	8,500	10,000
Benefits paid	(38,706)	(34,883)
Fair value of plan assets at end of year	479,025	596,806	$ 528,881
Reconciliation:
Funded status	29,498	777
Unrecognized prior service cost	0	0
Unrecognized net loss	0	0
Net amount recognized	$ 29,498	$ 777