Details of Selected Financial Statement Captions - Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024
Balance Sheet Related Disclosures [Abstract]
Deferred gas costs	$ 140,626	$ 159,762
Winter Storm Uri incremental costs	5,841	3,949
Prepaid expenses	80,495	74,780
Taxes receivable	8,948	14,332
Materials and supplies	20,076	16,961
Assets from risk management activities	5,303	2,091
Regulatory assets (See Note 3)	33,311	12,297
Other	7,027	3,896
Total	$ 301,627	$ 288,068