Supplementary Information For Oil And Gas Producing Activities (Capitalized Costs Relating To Oil And Gas Producing Activities) (Details) - USD ($) $ in Thousands		Sep. 30, 2020	Sep. 30, 2019
Supplementary Information For Oil And Gas Producing Activities Unaudited [Abstract]
Proved Properties	[1]	$ 6,238,830	$ 5,623,623
Unproved Properties		148,075	53,498
Capitalized Costs, Oil and Gas Producing Activities, Gross, Total		6,386,905	5,677,121
Less - Accumulated Depreciation, Depletion and Amortization		4,628,765	4,012,568
Capitalized Costs Oil And Gas Producing Activities Net		1,758,140	1,664,553
Asset retirement costs		$ 132,600	$ 70,500

[1] Includes asset retirement costs of $132.6 million and $70.5 million at September 30, 2020 and 2019, respectively.