Supplementary Information For Oil And Gas Producing Activities (Capitalized Costs Relating To Oil And Gas Producing Activities) (Details) - USD ($) $ in Thousands		Sep. 30, 2015	Sep. 30, 2014
Supplementary Information For Oil And Gas Producing Activities Unaudited [Abstract]
Proved Properties	[1]	$ 4,473,721	$ 3,941,143
Unproved Properties		176,327	141,719
Capitalized Costs, Oil and Gas Producing Activities, Gross, Total		4,650,048	4,082,862
Less - Accumulated Depreciation, Depletion and Amortization		2,572,348	1,211,610
Capitalized Costs Oil And Gas Producing Activities Net		2,077,700	2,871,252
Asset retirement costs		$ 113,300	$ 75,700

[1] Includes asset retirement costs of $113.3 million and $75.7 million at September 30, 2015 and 2014, respectively.