Supplementary Information For Oil And Gas Producing Activities (Principal Sources Of Change In The Standardized Measure Of Discounted Future Net Cash Flows) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Supplementary Information For Oil And Gas Producing Activities Unaudited [Abstract]
Standardized Measure of Discounted Future Net Cash Flows at Beginning of Year	$ 1,222,470	$ 1,736,319	$ 1,720,305
Sales, Net of Production Costs	(626,132)	(290,975)	(425,773)
Net Changes in Prices, Net of Production Costs	1,478,995	(1,109,101)	(164,428)
Extensions and Discoveries	462,040	4,236	202,683
Changes in Estimated Future Development Costs	48,247	99,884	(69,254)
Purchases of Minerals in Place	0	170,363	0
Sales of Minerals in Place	0	0	0
Previously Estimated Development Costs Incurred	81,239	219,938	245,964
Net Change in Income Taxes at Applicable Statutory Rate	(415,993)	248,182	21,370
Revisions of Previous Quantity Estimates	(52,383)	(28,337)	53,777
Accretion of Discount and Other	155,089	171,961	151,675
Standardized Measure of Discounted Future Net Cash Flows at End of Year	$ 2,353,572	$ 1,222,470	$ 1,736,319