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Supplemental Oil And Gas Information (Schedule Of Oil And Gas Property Acquisition, Exploration And Development) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Supplemental Oil And Gas Information [Abstract]      
Property acquisitions unproved $ 93 $ 8 $ 90
Exploration cost 69 396 22
Development cost     252
Total $ 162 $ 404 $ 364