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Supplemental Oil And Gas Information (Schedule Of Reserve Value By Category And The Respective Present Values, Before Income Taxes, Discounted At 10% As A Percentage Of Total Proved Reserves) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Reserve Quantities [Line Items] |  |  |
Total proved reserves year-end reserve report | $ 8,170 | $ 5,815 | $ 8,287
Proved developed producing reserves (PDP) | $ 7,065 | $ 5,397 | $ 7,686
% of PDP reserves to total proved reserves | 87.00% | 93.00% | 93.00%
Proved developed non-producing reserves | $ 1,082 | $ 418 | $ 601
% of PDNP reserves to total proved reserves | 13.00% | 7.00% | 7.00%
Proved undeveloped reserves (PUD) | $ 23 |  |
Oil [Member] |  |  |
Reserve Quantities [Line Items] |  |  |
Total proved reserves year-end reserve report | 8,170 | $ 5,815 | $ 8,287
Proved developed producing reserves (PDP) | $ 7,065 | $ 5,397 | $ 7,686
% of PDP reserves to total proved reserves | 87.00% | 93.00% | 93.00%
Proved developed non-producing reserves | $ 1,082 | $ 418 | $ 601
% of PDNP reserves to total proved reserves | 13.00% | 7.00% | 7.00%
Proved undeveloped reserves (PUD) | $ 23 |  |

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