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, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Supplementary Information For Oil And Gas Producing Activities Unaudited [Abstract]
Future Cash Inflows	$ 6,144,317	$ 3,768,463	$ 6,916,775
Future Production Costs	2,378,262	1,994,916	2,854,142
Future Development Costs	411,578	375,152	761,922
Future Income Tax Expense at Applicable Statutory Rate	1,160,469	303,397	1,117,433
Future Net Cash Flows	2,194,008	1,094,998	2,183,278
10% Annual Discount for Estimated Timing of Cash Flows	1,080,962	452,470	860,244
Standardized Measure of Discounted Future Net Cash Flows	$ 1,113,046	$ 642,528	$ 1,323,034	$ 2,066,878