Interim Pension and Other Postretirement Benefit Plan Information - Schedule of Components of Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,837	$ 2,405	$ 5,674	$ 4,794
Interest cost	6,663	7,430	13,326	14,926
Expected return on assets	(7,655)	(7,202)	(15,309)	(14,404)
Amortization of prior service cost (credit)	0	0	0	0
Amortization of actuarial (gain) loss	256	97	511	215
Settlements			0	776
Net periodic pension cost	2,101	2,730	4,202	6,307
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	2,033	1,507	4,066	3,014
Interest cost	3,365	3,509	6,731	7,017
Expected return on assets	(3,831)	(3,128)	(7,663)	(6,256)
Amortization of prior service cost (credit)	(3,260)	(3,260)	(6,520)	(6,520)
Amortization of actuarial (gain) loss	(2,429)	(2,718)	(4,858)	(5,436)
Settlements			0	0
Net periodic pension cost	$ (4,122)	$ (4,090)	$ (8,244)	$ (8,181)