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Supplemental Financial Information Exploration and Production (Details 4) (Details) | 12 Months Ended
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Dec. 31, 2011 Mcfe | Dec. 31, 2010 Mcfe | Dec. 31, 2009 Mcfe
Proved Developed and Undeveloped Reserves [Roll Forward] |  |  |
Proved developed and undeveloped reserves, starting balance | 645,596,000 | 653,724,000 | 810,371,000
Proved Developed and Undeveloped Reserves, Production | (66,596,000) | (69,963,000) | (75,299,000)
Proved Developed and Undeveloped Reserves, Extensions, Discoveries, and Additions | 65,049,000 | 56,523,000 | 42,297,000
Proved Developed and Undeveloped Reserves, Improved Recovery | 0 | 0 | 0
Proved Developed and Undeveloped Reserves, Purchases of Minerals in Place | 1,486,000 | 60,991,000 | 0
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place | 0 | (202,000) | (1,510,000)
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates | (59,627,000) | (55,477,000) | (122,135,000)
Proved developed and undeveloped reserves, ending balance | 585,908,000 | 645,596,000 | 653,724,000
Reduction in proved undeveloped reserves | 53,600,000 |  |
Natural Gas Reserves [Member] |  |  |
Proved Developed and Undeveloped Reserves [Roll Forward] |  |  |
Proved developed and undeveloped reserves, starting balance | 448,397 | 448,425 | 604,282
Proved Developed and Undeveloped Reserves, Production | (45,598) | (50,391) | (56,632)
Proved Developed and Undeveloped Reserves, Extensions, Discoveries, and Additions | 28,221 | 36,191 | 26,882
Proved Developed and Undeveloped Reserves, Improved Recovery | 0 | 0 | 0
Proved Developed and Undeveloped Reserves, Purchases of Minerals in Place | 54 | 55,119 | 0
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place | 0 | (92) | (22)
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates | (51,247) | (40,855) | (126,085)
Proved developed and undeveloped reserves, ending balance | 379,827 | 448,397 | 448,425
Oil Reserves [Member] |  |  |
Proved Developed and Undeveloped Reserves [Roll Forward] |  |  |
Proved developed and undeveloped reserves, starting balance | 32,867 | 34,216 | 34,348
Proved Developed and Undeveloped Reserves, Production | (3,500) | (3,262) | (3,111)
Proved Developed and Undeveloped Reserves, Extensions, Discoveries, and Additions | 6,138 | 3,389 | 2,569
Proved Developed and Undeveloped Reserves, Improved Recovery | 0 | 0 | 0
Proved Developed and Undeveloped Reserves, Purchases of Minerals in Place | 239 | 979 | 0
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place | 0 | (18) | (248)
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates | (1,397) | (2,437) | 658
Proved developed and undeveloped reserves, ending balance | 34,347 | 32,867 | 34,216

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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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- Definition Changes in proved reserve estimates resulting from application of improved recovery techniques. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 59F -Subparagraph b -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 (b) -URI http://asc.fasb.org/extlink&oid=6821537&loc=d3e61831-109447 + Details
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- Definition The net quantity of proved reserves as of the balance sheet date. Proved oil reserves are the estimated quantities of crude oil and natural gas liquids which geological and engineering data demonstrate with reasonable certainty to be recoverable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-10.(a)(2)) -URI http://asc.fasb.org/extlink&oid=6949603&loc=d3e511914-122862 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 59F -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 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 4 -Section 10 -Paragraph a -Subparagraph 2 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6821537&loc=d3e61831-109447 + Details
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- Definition Production of proved reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 59F -Subparagraph e -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 (e) -URI http://asc.fasb.org/extlink&oid=6821537&loc=d3e61831-109447 + Details
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- Definition Purchase of minerals in place. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 59F -Subparagraph c -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 (c) -URI http://asc.fasb.org/extlink&oid=6821537&loc=d3e61831-109447 + Details
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- Definition Revisions represent changes in previous estimates of proved reserves, either upward or downward, resulting from new information (except for an increase in proved acreage) normally obtained from development drilling and production history or resulting from change in economic factors. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 59F -Subparagraph a -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 (a) -URI http://asc.fasb.org/extlink&oid=6821537&loc=d3e61831-109447 + Details
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