Securitization - Schedule of Consolidated Statement of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Variable Interest Entity [Line Items]
Operating revenues	$ 1,175,999	$ 1,158,467
Operation and maintenance expense	(207,044)	(166,345)
Amortization expense	(180,533)	(164,608)
Interest expense, net	(52,925)	(51,875)
Income before income taxes	431,189	365,116
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Operating revenues	3,393	3,333
Operation and maintenance expense	(61)	0
Amortization expense	(2,264)	(2,166)
Interest expense, net	(1,068)	(1,167)
Income before income taxes	$ 0	$ 0