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Supplemental Oil And Gas Reserve Information - Unaudited (Narrative) (Details) (USD $) | 12 Months Ended | 1 Months Ended | 12 Months Ended
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Dec. 31, 2011 MBoe | Dec. 31, 2010 MBoe | Dec. 31, 2009 MBoe | Dec. 31, 2008 | Nov. 30, 2010 Roosevelt County [Member] | Dec. 31, 2010 Richland County [Member] | Dec. 31, 2009 Kerogen [Member] | Dec. 31, 2009 Fidelity [Member] | Dec. 31, 2011 MBoe [Member] | Dec. 31, 2010 MBoe [Member] | Dec. 31, 2009 MBoe [Member]
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |  |  |  |
Purchases of reserves in place |  |  |  |  | 715 | 764 | 1,511 | 484 | 111 | 1,479 | 1,995
Extensions, discoveries and other additions | 43,168 |  |  |  |  |  |  |  | 43,168 | 24,473 | 8,950
Estimated extensions and discoveries of reserves associated with new wells | 12,696 | 8,122 | 1,508 |  |  |  |  |  |  |  |
Percentage of reserves produced from wells in certain formations | 100.00% | 99.00% | 95.00% |  |  |  |  |  |  |  |
Percentage of proved undeveloped reserves | 100.00% | 100.00% | 100.00% |  |  |  |  |  |  |  |
Additional proved undeveloped reserves | 30,472 | 16,351 | 7,442 |  |  |  |  |  |  |  |
Number of traded interests in non-operated properties |  | 3 |  |  |  |  |  |  |  |  |
Remaining reserves |  |  |  |  |  |  |  |  | (142) | (123) | (5)
Net positive revisions of previous estimates |  |  |  |  |  |  |  |  | (288) | 2,552 | 767
Percentage of revisions due to decrease in oil prices | 0.72% |  |  |  |  |  |  |  |  |  |
Percentage of revisions due to increase in oil prices |  | 29.00% |  |  |  |  |  |  |  |  |
Percentage of revisions due to higher working interests in proved wells | 29.00% |  |  |  |  |  |  |  |  |  |
Unweighted arithmetic average first-day-of-the-month prices for oil, price per Bbl | $ 96.23 | $ 79.40 | $ 61.04 |  |  |  |  |  |  |  |
Market price of oil |  |  |  | $ 44.60 |  |  |  |  |  |  |
Unweighted arithmetic average first-day-of-the-month prices for natural gas, price per MMBtu | $ 4.12 | $ 4.38 | $ 3.87 |  |  |  |  |  |  |  |
Percentage of revisions to estimates due to other changes |  | 42.00% |  |  |  |  |  |  |  |  |
Discount rate of future cash flows | 10.00% |  |  |  |  |  |  |  |  |  |

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- Definition Additions to proved reserves that result from (1) extension of the proved acreage of previously discovered (old) reservoirs through additional drilling in periods after discovery and (2) discovery of new fields with proved reserves or of new reservoirs of proved reserves in old fields. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 59F -Subparagraph d -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. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 5 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6821537&loc=d3e61831-109447 + Details
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