Regulation - Narrative (Details) - USD ($) $ in Thousands			1 Months Ended	12 Months Ended
	Mar. 23, 2023	Sep. 01, 2022	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2021
Regulatory Assets [Line Items]
Regulatory assets				$ 579,390	$ 554,928
Winter Storm Uri incremental costs
Regulatory Assets [Line Items]
Regulatory assets				10,373	$ 32,115
Texas | Winter Storm Uri
Regulatory Assets [Line Items]
Regulatory assets						$ 2,020,000
Texas | Winter Storm Uri | Extraordinary Gas Cost
Regulatory Assets [Line Items]
Regulatory asset, authorized			$ 3,500,000
Regulatory asset, proceeds from customer rate relief bonds	$ 2,020,000		$ 2,020,000
Texas | Winter Storm Uri | Extraordinary Gas Cost | Minimum
Regulatory Assets [Line Items]
Regulatory asset, maturity period			12 years
Texas | Winter Storm Uri | Extraordinary Gas Cost | Maximum
Regulatory Assets [Line Items]
Regulatory asset, maturity period			18 years
Texas | Winter Storm Uri | Winter Storm Uri incremental costs
Regulatory Assets [Line Items]
Regulatory asset, deferred costs		$ 32,400
Regulatory asset, recovering cost				22,000
Regulatory asset, deferred costs, remaining				10,400
Texas | Winter Storm Uri | Winter Storm Uri incremental costs | Other current assets
Regulatory Assets [Line Items]
Regulatory asset, deferred costs, remaining				4,000
Texas | Winter Storm Uri | Winter Storm Uri incremental costs | Deferred charges and other assets
Regulatory Assets [Line Items]
Regulatory asset, deferred costs, remaining				$ 6,400