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, 2020	Sep. 30, 2019	Sep. 30, 2018
Supplementary Information For Oil And Gas Producing Activities Unaudited [Abstract]
Standardized Measure of Discounted Future Net Cash Flows at Beginning of Year	$ 1,736,319	$ 1,720,305	$ 1,113,046
Sales, Net of Production Costs	(290,975)	(425,773)	(381,775)
Net Changes in Prices, Net of Production Costs	(1,109,101)	(164,428)	541,021
Extensions and Discoveries	4,236	202,683	212,494
Changes in Estimated Future Development Costs	99,884	(69,254)	(43,771)
Purchases of Minerals in Place	170,363	0	0
Sales of Minerals in Place	0	0	(100,816)
Previously Estimated Development Costs Incurred	219,938	245,964	182,348
Net Change in Income Taxes at Applicable Statutory Rate	248,182	21,370	55,558
Revisions of Previous Quantity Estimates	(28,337)	53,777	61,363
Accretion of Discount and Other	171,961	151,675	80,837
Standardized Measure of Discounted Future Net Cash Flows at End of Year	$ 1,222,470	$ 1,736,319	$ 1,720,305