Interim Pension and Other Postretirement Benefit Plan Information - Schedule of Components of Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,838	$ 2,405	$ 8,512	$ 7,199
Interest cost	6,663	7,430	19,989	22,356
Expected return on assets	(7,655)	(7,202)	(22,964)	(21,606)
Amortization of prior service cost (credit)	0	0	0	0
Amortization of actuarial (gain) loss	256	97	767	313
Settlements			0	776
Net periodic pension cost	2,102	2,730	6,304	9,038
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	2,033	1,507	6,099	4,521
Interest cost	3,365	3,509	10,096	10,526
Expected return on assets	(3,831)	(3,128)	(11,494)	(9,383)
Amortization of prior service cost (credit)	(3,260)	(3,260)	(9,780)	(9,780)
Amortization of actuarial (gain) loss	(2,429)	(2,718)	(7,287)	(8,154)
Settlements			0	0
Net periodic pension cost	$ (4,122)	$ (4,090)	$ (12,366)	$ (12,270)