Securitization - Schedule of Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Variable Interest Entity [Line Items]
Operating revenues	$ 1,342,585	$ 1,175,999
Operation and maintenance expense	(229,810)	(207,044)
Amortization expense	(194,645)	(180,533)
Interest expense, net	(33,413)	(52,925)
Income before income taxes	503,582	431,189
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Operating revenues	3,302	3,393
Operation and maintenance expense	0	(61)
Amortization expense	(2,329)	(2,264)
Interest expense, net	(973)	(1,068)
Income before income taxes	$ 0	$ 0