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, 2018	Dec. 31, 2017	Dec. 31, 2016
Reserve Quantities [Line Items]
Sales and transfers of oil and natural gas produced, net of production costs	$ (297,791)	$ (239,953)	$ (173,920)
Net changes in prices and production costs	120,062	236,126	(94,026)
Revisions in quantity estimates and changes in production timing	(33,282)	87,239	(51,979)
Extensions, discoveries, and improved recovery, less related costs	234,172	102,965	84,738
Changes in estimated future development costs	19,535	(5,194)	70,976
Previously estimated cost incurred during the period	63,557	36,044	16,602
Purchases of minerals in place	23,416	51,686	2,652
Sales of minerals in place	(5,004)	(1,447)	(17,248)
Accretion of discount	89,753	57,517	69,069
Net change in income taxes	(31,674)	(33,389)	44,241
Other-net	(6,236)	(2,634)	(22,381)
Net change	176,508	288,960	(71,276)
Beginning of year	807,170	518,210	589,486
End of year	$ 983,678	$ 807,170	$ 518,210