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, 2016	Sep. 30, 2015	Sep. 30, 2014
Supplementary Information For Oil And Gas Producing Activities Unaudited [Abstract]
Standardized Measure of Discounted Future Net Cash Flows at Beginning of Year	$ 1,323,034	$ 2,066,878	$ 1,966,366
Sales, Net of Production Costs	(218,444)	(318,753)	(626,960)
Net Changes in Prices, Net of Production Costs	(1,066,593)	(1,752,843)	(38,723)
Extensions and Discoveries	47,742	266,159	381,008
Changes in Estimated Future Development Costs	143,752	164,510	68,731
Purchases of Minerals in Place	0	0	34,705
Sales of Minerals in Place	(95,849)	(1)	(691)
Previously Estimated Development Costs Incurred	92,840	161,833	179,502
Net Change in Income Taxes at Applicable Statutory Rate	387,739	545,442	(231,807)
Revisions of Previous Quantity Estimates	6,202	(16,573)	55,184
Accretion of Discount and Other	22,105	206,382	279,563
Standardized Measure of Discounted Future Net Cash Flows at End of Year	$ 642,528	$ 1,323,034	$ 2,066,878