Supplementary Information For Oil And Gas Producing Activities (Capitalized Costs Relating To Oil And Gas Producing Activities) (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Sep. 30, 2015
Supplementary Information For Oil And Gas Producing Activities Unaudited [Abstract]
Proved Properties	[1]	$ 4,554,929	$ 4,473,721
Unproved Properties		135,285	176,327
Capitalized Costs, Oil and Gas Producing Activities, Gross, Total		4,690,214	4,650,048
Less - Accumulated Depreciation, Depletion and Amortization		3,657,239	2,572,348
Capitalized Costs Oil And Gas Producing Activities Net		1,032,975	2,077,700
Asset retirement costs		$ 63,600	$ 113,300

[1] Includes asset retirement costs of $63.6 million and $113.3 million at September 30, 2016 and 2015, respectively.