Variable Interest Entity - Schedule of Consolidated Statement of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Variable Interest Entity [Line Items]
Operating revenues	$ 701,549	$ 662,733	$ 3,507,243	$ 3,687,715
Operation and maintenance expense	(211,309)	(195,049)	(577,553)	(574,781)
Amortization expense	(166,827)	(150,726)	(496,522)	(445,063)
Interest expense, net	(41,160)	(31,334)	(148,477)	(105,464)
Income before income taxes	199,005	$ 154,089	1,076,356	$ 862,380
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Operating revenues	3,463		10,265
Operation and maintenance expense	(52)		(276)
Amortization expense	(2,292)		(6,561)
Interest expense, net	(1,119)		(3,428)
Income before income taxes	$ 0		$ 0