Details of Selected Consolidated Balance Sheet Captions - Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Balance Sheet Related Disclosures [Abstract]
Deferred gas costs	$ 66,395	$ 40,593
Winter storm Uri incremental costs	2,011,719	0
Prepaid expenses	48,766	40,340
Materials and supplies	15,581	6,829
Assets from risk management activities	55,073	5,687
Other	3,375	14,456
Total	2,200,909	$ 107,905
Gas purchases, current	2,003,700
Deferred non cash carrying costs, current	$ 8,000