Supplementary Information For Oil And Gas Producing Activities (Standardized Measure Of Discounted Future Net Cash Flows Relating To Proved Oil And Gas Reserves) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Supplementary Information For Oil And Gas Producing Activities Unaudited [Abstract]
Future Cash Inflows	$ 6,493,362	$ 8,738,182	$ 7,822,855
Future Production Costs	3,149,857	2,989,518	2,606,411
Future Development Costs	501,678	797,640	559,707
Future Income Tax Expense at Applicable Statutory Rate	454,553	1,159,882	1,125,910
Future Net Cash Flows	2,387,274	3,791,142	3,530,827
10% Annual Discount for Estimated Timing of Cash Flows	1,164,804	2,054,823	1,810,522
Standardized Measure of Discounted Future Net Cash Flows	$ 1,222,470	$ 1,736,319	$ 1,720,305	$ 1,113,046