Revenue and Accounts Receivable - Narrative (Details) $ in Thousands	3 Months Ended	12 Months Ended			30 Months Ended
	Dec. 31, 2023 USD ($)	Sep. 30, 2024 USD ($) state	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2024 USD ($) state	Nov. 30, 2023
Disaggregation of Revenue [Line Items]
Number of states excluded due to gas cost recovery mechanisms | state		6			6
Percent of customers excluded due to gas cost recovery mechanisms		89.00%
Reduction to bad debt expense		$ (24,843)	$ (22,353)	$ (16,576)
Recovery of uncollectible accounts, not yet been written off		4,192
Mississippi Public Service Commission
Disaggregation of Revenue [Line Items]
Recovery of uncollectible accounts, term	2 years					1 year
Reduction to bad debt expense	$ 13,900
Recovery of uncollectible accounts, previously written off but not yet recovered through rates					$ 9,700
Recovery of uncollectible accounts, not yet been written off		$ 4,200
Pipeline and Storage
Disaggregation of Revenue [Line Items]
Regulatory mechanism threshold (in percent)		75.00%