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, 2019	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Supplementary Information For Oil And Gas Producing Activities Unaudited [Abstract]
Future Cash Inflows	$ 8,738,182	$ 7,822,855	$ 6,144,317
Future Production Costs	2,989,518	2,606,411	2,378,262
Future Development Costs	797,640	559,707	411,578
Future Income Tax Expense at Applicable Statutory Rate	1,159,882	1,125,910	1,160,469
Future Net Cash Flows	3,791,142	3,530,827	2,194,008
10% Annual Discount for Estimated Timing of Cash Flows	2,054,823	1,810,522	1,080,962
Standardized Measure of Discounted Future Net Cash Flows	$ 1,736,319	$ 1,720,305	$ 1,113,046	$ 642,528