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, 2025	Sep. 30, 2024	Sep. 30, 2023
Standardized Measure of Discounted Future Net Cash Flows [Roll Forward]
Standardized Measure of Discounted Future Net Cash Flows at Beginning of Year	$ 1,336,455	$ 2,572,108	$ 5,448,330
Sales, Net of Production Costs	(802,983)	(456,506)	(767,487)
Net Changes in Prices, Net of Production Costs	1,716,936	(1,829,714)	(3,918,392)
Extensions and Discoveries	330,925	(11,007)	237,057
Changes in Estimated Future Development Costs	58,606	32,990	(222,233)
Purchases of Minerals in Place	0	0	34,346
Sales of Minerals in Place	0	0	0
Previously Estimated Development Costs Incurred	246,309	305,602	342,024
Net Change in Income Taxes at Applicable Statutory Rate	(467,758)	462,075	959,728
Revisions of Previous Quantity Estimates	(7,374)	19,216	33,192
Accretion of Discount and Other	343,268	241,691	425,543
Standardized Measure of Discounted Future Net Cash Flows at End of Year	$ 2,754,384	$ 1,336,455	$ 2,572,108