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Oil And Gas Properties (Narrative) (Details) - USD ($)
3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Oil And Gas Properties [Abstract]                
Depletion expense           $ 796,000 $ 1,000,000 $ 2,500,000
Impairment $ 0 $ 0 $ 0 $ 0 $ 0   $ 2,805,000 $ 14,526,000