Supplementary Information for Exploration and Production Activities - Principal Sources of Change in the Standardized Measure of Discounted Future Net Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Standardized Measure of Discounted Future Net Cash Flows [Roll Forward]
Standardized Measure of Discounted Future Net Cash Flows at Beginning of Year	$ 2,572,108	$ 5,448,330	$ 2,353,572
Sales, Net of Production Costs	(456,506)	(767,487)	(1,572,402)
Net Changes in Prices, Net of Production Costs	(1,829,714)	(3,918,392)	4,132,889
Extensions and Discoveries	(11,007)	237,057	1,355,257
Changes in Estimated Future Development Costs	32,990	(222,233)	(32,160)
Purchases of Minerals in Place	0	34,346	0
Sales of Minerals in Place	0	0	(311,308)
Previously Estimated Development Costs Incurred	305,602	342,024	154,253
Net Change in Income Taxes at Applicable Statutory Rate	462,075	959,728	(1,180,349)
Revisions of Previous Quantity Estimates	19,216	33,192	3,316
Accretion of Discount and Other	241,691	425,543	545,262
Standardized Measure of Discounted Future Net Cash Flows at End of Year	$ 1,336,455	$ 2,572,108	$ 5,448,330