Supplemental Oil And Gas Information (Schedule Of Changes In The Standardized Measure Of Discounted Future Net Cash Flows From Proved Oil And Gas Reserves) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Supplemental Oil And Gas Information [Abstract]
Balance, beginning of year	$ 8,365	$ 13,976	$ 8,170
Sales, net of production costs and taxes	(210)	(1,646)	(2,611)
Discoveries and extensions, net of costs		154	798
Purchase of reserves in place			143
Sale of reserves in place		(26)
Net changes in prices and production costs	(2,893)	(3,348)	4,304
Revisions of quantity estimates	(2,353)	(3,058)	2,180
Previously estimated development cost incurred during the year			210
Changes in future development costs	(314)	1,016	78
Changes in timing and other	(389)	86	(4)
Accretion of discount	691	1,211	708
Net change in income taxes
Balance, end of year	$ 2,897	$ 8,365	$ 13,976