Supplemental Oil And Gas Disclosures (Schedule Of Principal Sources Of Changes In Standardized Measure Of Discounted Future Net Cash Flows) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Reserve Quantities [Line Items]
Sales and transfers of oil and natural gas produced, net of production costs	$ (84,163)	$ (200,233)
Net changes in prices and production costs	(165,978)	(508,066)
Revisions in quantity estimates and changes in production timing	(50,979)	(338,994)
Extensions, discoveries, and improved recovery, less related costs	2,827	53,123
Changes in estimated future development costs	0	311,190
Previously estimated cost incurred during the period	0	64,362
Purchases of minerals in place	852	6,416
Sales of minerals in place	(46)	(25,813)
Accretion of discount	46,203	110,571
Net change in income taxes	282	121,708
Other-net	(17,686)	(116,233)
Net change	(268,688)	(521,969)
Beginning of year	461,709	983,678
End of year	$ 193,021	$ 461,709