Interim Pension and Other Postretirement Benefit Plan Information - Schedule of Components of Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,389	$ 2,908
Interest cost	7,497	7,325
Expected return on assets	(7,202)	(7,278)
Amortization of prior service cost (credit)	0	(30)
Amortization of actuarial (gain) loss	118	164
Settlements	(776)	0
Net periodic pension cost	3,578	3,089
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1,507	1,546
Interest cost	3,509	3,478
Expected return on assets	(3,128)	(2,804)
Amortization of prior service cost (credit)	(3,260)	(3,285)
Amortization of actuarial (gain) loss	(2,718)	(1,863)
Settlements	0	0
Net periodic pension cost	$ (4,090)	$ (2,928)