Supplementary Information For Oil And Gas Producing Activities (Capitalized Costs Relating To Oil And Gas Producing Activities) (Details) - USD ($) $ in Thousands		Sep. 30, 2017	Sep. 30, 2016
Supplementary Information For Oil And Gas Producing Activities Unaudited [Abstract]
Proved Properties	[1]	$ 4,832,301	$ 4,554,929
Unproved Properties		80,932	135,285
Capitalized Costs, Oil and Gas Producing Activities, Gross, Total		4,913,233	4,690,214
Less - Accumulated Depreciation, Depletion and Amortization		3,765,710	3,657,239
Capitalized Costs Oil And Gas Producing Activities Net		1,147,523	1,032,975
Asset retirement costs		$ 54,400	$ 63,600

[1] Includes asset retirement costs of $54.4 million and $63.6 million at September 30, 2017 and 2016, respectively.