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Supplemental Oil and Natural Gas Reserve Data (unaudited) (Proved Developed and Undeveloped Reserves) (Details)
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12 Months Ended | |||
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Dec. 31, 2012
MBoe
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Dec. 31, 2011
MBoe
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Dec. 31, 2010
MBoe
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Dec. 31, 2009
MBoe
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| Proved developed and undeveloped reserves: | ||||
| Beginning of period | 6,735,000 | 7,003,000 | 6,622,000 | 6,396,000 |
| End of period | 6,735,000 | 7,003,000 | 6,622,000 | 6,396,000 |
| Beginning of period | 7,337,000 | 8,925,000 | 7,019,000 | 3,267,000 |
| End of period | 7,337,000 | 8,925,000 | 7,019,000 | 3,267,000 |
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Crude Oil [Member]
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| Proved developed and undeveloped reserves: | ||||
| Beginning of period | 10,075,000 | 8,149,000 | 6,479,000 | |
| Revisions to previous estimates | (488,000) | (110,000) | 423,000 | |
| Change in ownership | 0 | 0 | 0 | |
| Purchase of reserves in place | 38,000 | 0 | 0 | |
| Sale of reserves in place | (504,000) | (30,000) | 0 | |
| Extensions and discoveries | 2,636,000 | 3,062,000 | 2,106,000 | |
| Production | (977,000) | (996,000) | (859,000) | |
| End of period | 10,780,000 | 10,075,000 | 8,149,000 | |
| Beginning of period | 5,069,000 | 4,503,000 | 4,346,000 | |
| End of period | 4,955,000 | 5,069,000 | 4,503,000 | |
| Beginning of period | 5,006,000 | 3,645,000 | 2,133,000 | |
| End of period | 5,825,000 | 5,006,000 | 3,645,000 | |
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Natural Gas [Member]
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| Proved developed and undeveloped reserves: | ||||
| Beginning of period | 35,118,000,000 | 32,957,000,000 | 19,103,000,000 | |
| Revisions to previous estimates | (10,838,000,000) | 486,000,000 | 354,000,000 | |
| Change in ownership | 0 | 0 | 0 | |
| Purchase of reserves in place | 115,000,000 | 0 | 0 | |
| Sale of reserves in place | (4,404,000,000) | (308,000,000) | 0 | |
| Extensions and discoveries | 3,350,000,000 | 7,064,000,000 | 18,392,000,000 | |
| Production | (3,588,000,000) | (5,081,000,000) | (4,892,000,000) | |
| End of period | 19,753,000,000 | 35,118,000,000 | 32,957,000,000 | |
| Beginning of period | 11,605,000,000 | 12,715,000,000 | 12,301,000,000 | |
| End of period | 10,680,000,000 | 11,605,000,000 | 12,715,000,000 | |
| Beginning of period | 23,513,000,000 | 20,241,000,000 | 6,802,000,000 | |
| End of period | 9,073,000,000 | 23,513,000,000 | 20,241,000,000 | |
| X | ||||||||||
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- Definition
Proved Developed And Undeveloped Reserves Change in ownership No definition available.
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| X | ||||||||||
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- Definition
Energy measure of interests in proved developed reserves of crude oil, including condensate and natural gas liquids, natural gas, synthetic oil and gas, or other nonrenewable natural resource that is intended to be upgraded into synthetic oil and gas. No definition available.
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| X | ||||||||||
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- Definition
Proved Energy measure of proved undeveloped reserves of crude oil, including condensate and natural gas liquids, natural gas, synthetic oil and gas, or other nonrenewable natural resource that is intended to be upgraded into synthetic oil and gas. No definition available.
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| X | ||||||||||
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- Details
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| X | ||||||||||
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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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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- Definition
Production of proved reserves. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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- Definition
Purchase of minerals in place. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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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. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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- Definition
Sales of minerals in place. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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- Definition
Net quantities of an enterprise's interests in proved developed reserves of either crude oil (including condensate and natural gas liquids), natural gas, synthetic oil and gas, or other nonrenewable natural resource that is intended to be upgraded into synthetic oil and gas as of the beginning and the end of the year. "Net" quantities of reserves include those relating to the enterprise's operating and nonoperating interests in properties. Quantities of reserves relating to royalty interests owned are included in "net" quantities if the necessary information is available to the enterprise. "Net" quantities does not include reserves relating to interests of others in properties owned by the enterprise. The unit of measure for reserve quantities is defined as "barrels" for oil and synthetic oil reserves or "cubic feet" or "cubic meters" for natural gas and synthetic gas reserves. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
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- Definition
Net quantities of an enterprise's interests in proved undeveloped reserves of either crude oil (including condensate and natural gas liquids), natural gas, synthetic oil and gas, or other renewable natural resource that is intended to be upgraded into synthetic oil and gas as of the beginning and the end of the year. "Net" quantities of reserves include those relating to the enterprise's operating and nonoperating interests in properties. Quantities of reserves relating to royalty interests owned are included in "net" quantities if the necessary information is available to the enterprise. "Net" quantities does not include reserves relating to interests of others in properties owned by the enterprise. The unit of measure for reserve quantities is defined as "barrels" for oil and synthetic oil reserves or "cubic feet" or "cubic meters" for natural gas and synthetic gas reserves. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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