| **Concentration of Risk (Tables)**                 | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
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| **Concentration of Risk [Abstract]**               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
| Schedules of Concentration of Risk, by Risk Factor | The largest single non-affiliated purchasers of our production were as follows:   Percentage ofCrude OilSales Percentage ofTotal Oil, Gas & NGL SalesYear Ended December 31, 2012    Glencore Energy UK Ltd 39% 31%Shell (1) 17% 14%Year Ended December 31, 2011    Glencore Energy UK Ltd 24% 16%Shell (1) 17% 12%Year Ended December 31, 2010    Glencore Energy UK Ltd 17% 11% (1)   Includes sales to both Shell Trading (US) Company and Shell International Trading and Shipping Limited. |

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| - Definition
Tabular disclosure of the nature of a concentration, a benchmark to which it is compared, and the percentage that the risk is to the benchmark.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 21 -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13537-108611Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 21 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6442-108592Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 16 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6327-108592Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13531-108611Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Statement of Position (SOP) -Number 94-6 -Paragraph 21, 22, 23, 24, 25 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.
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