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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
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Supplemental Oil And Gas Information [Abstract] |  |  |
Balance, beginning of year | $ 5,815 | $ 8,287 | $ 34,531
Sales, net of production costs and taxes | (1,239) | (2,037) | (1,901)
Discoveries and extensions, net of costs | 123 | 35 | 5
Purchase of reserves in place |  |  |
Sale of reserves in place |  | (10) |
Net changes in prices and production costs | 1,780 | (863) | (16,009)
Revisions of quantity estimates | 1,611 | (412) | (22,431)
Previously estimated development cost incurred during the year |  |  |
Changes in future development costs | (228) | 196 | 4,890
Changes in timing and other | (164) | (20) | (56)
Accretion of discount | 472 | 639 | 3,373
Net change in income taxes |  |  | 5,885
Balance, end of year | $ 8,170 | $ 5,815 | $ 8,287

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- Definition Amount of decrease in standardized measure of discounted future net cash flow as a result of sales of minerals in place. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 + Details
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- Definition Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of extensions, discoveries and improved recovery of proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 + Details
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- Definition Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of revisions of estimated quantity of oil and gas in proved reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 35 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62500-109447 + Details
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