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, 2024	Dec. 31, 2023	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,405		$ 2,915	$ 7,199	$ 8,731
Interest cost	7,430		7,265	22,356	21,915
Expected return on assets	(7,202)		(7,278)	(21,606)	(21,835)
Amortization of prior service cost (credit)	0		(30)	0	(91)
Amortization of actuarial (gain) loss	97		178	313	506
Settlements	0	$ (800)	(1,030)	(776)	(1,030)
Net periodic pension cost	2,730		4,080	9,038	10,256
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1,507		1,546	4,521	4,637
Interest cost	3,509		3,478	10,526	10,433
Expected return on assets	(3,128)		(2,804)	(9,383)	(8,411)
Amortization of prior service cost (credit)	(3,260)		(3,285)	(9,780)	(9,856)
Amortization of actuarial (gain) loss	(2,718)		(1,863)	(8,154)	(5,589)
Settlements	0		0	0	0
Net periodic pension cost	$ (4,090)		$ (2,928)	$ (12,270)	$ (8,786)