Details of Selected Financial Statement Captions - Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Balance Sheet Related Disclosures [Abstract]
Deferred gas costs	$ 148,297	$ 119,742
Winter Storm Uri incremental costs	21,213	2,020,954
Prepaid expenses	58,029	58,551
Taxes receivable	13,918	11,911
Materials and supplies	34,297	25,880
Assets from risk management activities	4,071	26,207
Other	12,211	11,245
Total	$ 292,036	$ 2,274,490