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, 2015	Sep. 30, 2014	Sep. 30, 2013
Supplementary Information For Oil And Gas Producing Activities Unaudited [Abstract]
Standardized Measure of Discounted Future Net Cash Flows at Beginning of Year	$ 2,066,878	$ 1,966,366	$ 1,469,791
Sales, Net of Production Costs	(318,753)	(626,960)	(526,630)
Net Changes in Prices, Net of Production Costs	(1,752,843)	(38,723)	339,655
Extensions and Discoveries	266,159	381,008	390,255
Changes in Estimated Future Development Costs	164,510	68,731	6,117
Purchases of Minerals in Place	0	34,705	0
Sales of Minerals in Place	(1)	(691)	0
Previously Estimated Development Costs Incurred	161,833	179,502	148,535
Net Change in Income Taxes at Applicable Statutory Rate	545,442	(231,807)	(130,574)
Revisions of Previous Quantity Estimates	(16,573)	55,184	34,864
Accretion of Discount and Other	206,382	279,563	234,353
Standardized Measure of Discounted Future Net Cash Flows at End of Year	$ 1,323,034	$ 2,066,878	$ 1,966,366