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Supplemental Oil And Gas Information (Schedule Of Results Of Operations From Oil And Gas Producing Activities) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Supplemental Oil And Gas Information [Abstract]      
Revenues $ 4,683 $ 4,113 $ 5,631
Production costs and taxes (3,444) (3,064) (3,731)
Depreciation, depletion and amortization (796) (1,009) (2,538)
Impairment   (2,805) (14,526)
Income (loss) from oil and gas producing activities $ 443 $ (2,765) $ (15,164)