Supplemental Oil And Gas Disclosures (Results Of Operations For Producing Activities) (Details) - USD ($) $ in Thousands	4 Months Ended	8 Months Ended	12 Months Ended
	Dec. 31, 2020	Aug. 31, 2020	Dec. 31, 2019
Supplemental Oil and Gas Disclosures [Abstract]
Revenues	$ 55,272	$ 96,033	$ 314,925
Production costs	(20,510)	(46,633)	(116,051)
Depreciation, depletion, amortization, and impairment	(40,840)	(461,901)	(727,529)
Results of operations, income before income taxes	(6,078)	(412,501)	(528,655)
Income tax (expense) benefit	128	6,698	101,952
Results of operations for producing activities (excluding corporate overhead and financing costs)	$ (5,950)	$ (405,803)	$ (426,703)