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Divestitures and Assets Held for Sale (Details) (USD $) | 12 Months Ended
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Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Disposal Group, Not Discontinued Operation, Disposal Disclosures [Abstract] |  |  |
Cash received on divestiture of non-strategic assets | $ (424,849,000) | $ (55,375,000) | $ (364,522,000)
Assets Held-for-sale, Current |  |  |
Reasonably certain period within which sale will take place (in years) | 1 |  |
Oil and gas properties held for sale, net of accumulated depletion, depreciation and amortization of $7,390 in 2013 and $20,676 in 2012 | 19,072,000 | 33,620,000 |
Asset Retirement Obligations Assets Held-for-sale Noncurrent | 3,033,000 | 1,393,000 |
Depletion, depreciation, amortization, and asset retirement obligation liability accretion | 822,872,000 | 727,877,000 | 511,103,000
Gain (Loss) on Sale of Proved Property | (27,974,000) | 27,018,000 | (220,676,000)
Mid Continent and Rocky Mountain Region |  |  |
Disposal Group, Not Discontinued Operation, Disposal Disclosures [Abstract] |  |  |
Cash received on divestiture of non-strategic assets |  | (57,900,000) |
Estimated gain on divestiture of assets |  | (7,400,000) |
South Texas and Gulf Coast Region |  |  |
Disposal Group, Not Discontinued Operation, Disposal Disclosures [Abstract] |  |  |
Cash received on divestiture of non-strategic assets |  |  | (230,700,000)
Estimated gain on divestiture of assets |  |  | (193,800,000)
Mid-Continent Divestiture |  |  |
Disposal Group, Not Discontinued Operation, Disposal Disclosures [Abstract] |  |  |
Cash received on divestiture of non-strategic assets | (370,300,000) |  | (35,800,000)
Estimated gain on divestiture of assets | (29,200,000) |  | (28,500,000)
Rocky Mountain Divestiture |  |  |
Disposal Group, Not Discontinued Operation, Disposal Disclosures [Abstract] |  |  |
Cash received on divestiture of non-strategic assets | (56,300,000) |  | (45,500,000)
Estimated gain on divestiture of assets | 10,100,000 |  | (27,200,000)
Permian Divestiture |  |  |
Disposal Group, Not Discontinued Operation, Disposal Disclosures [Abstract] |  |  |
Cash received on divestiture of non-strategic assets | (14,500,000) |  |
Estimated gain on divestiture of assets | (6,500,000) |  |
Oil and Gas Properties |  |  |
Assets Held-for-sale, Current |  |  |
Depletion, depreciation, amortization, and asset retirement obligation liability accretion |  | 1,700,000 |
Gain (Loss) on Sale of Proved Property |  | $ 33,900,000 |

X
- Definition Noncurrent portion of the carrying amount of a liability for an asset retirement obligation for an asset held for sale. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References No definition available. + Details
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- Definition Represents the period where there is reasonable certainty that the sale will take place for the assets to be classified as held for sale. + References No definition available. + Details
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- Definition The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets. Amount of accretion expense recognized in the income statement during the period that is associated with asset retirement obligations. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability. Such accretion expense representing changes in the liability for an asset retirement obligation due to passage of time is the result of applying an interest method of allocation to the amount of the liability at the beginning of the period. The interest rate used to measure that change shall be the credit-adjusted risk-free rate that existed when the liability, or portion thereof, was initially measured. That amount shall be recognized as an increase in the carrying amount of the liability and as an expense classified as an operating item in the statement of income. Accretion expense shall not be considered to be interest cost for purposes of capitalization of interest. + References No definition available. + Details
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- Definition Long-lived assets that are held for sale apart from normal operations and anticipated to be sold in less than one year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=6892542&loc=d3e1107-107759 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 144 -Paragraph 46 -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. + Details
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- Details
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- Definition Gain (loss) recorded from sale of oil and gas properties, includes the realized gains (losses) on the sale of proved and unproved oil and gas properties. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -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 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 41, 44, 45, 46, 47 -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. + Details
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- Definition The difference between the book value and the sale price of property that has been found to have proven oil and gas reserves. This element refers to the gain (loss). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -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 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585 + Details
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- Definition The cash inflow to dispose of long-lived, physical assets and mineral interests in oil and gas properties used for normal oil and gas operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 15 -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 FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3179-108585 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 16 -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. + Details
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