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Supplemental Financial Information Exploration and Production (Details 7) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items] |  |  |
Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Beginning Balance | $ 896,100 | $ 658,800 | $ 969,800
Sales and Transfers of Oil and Gas Produced, Net of Production Costs | (301,500) | (270,000) | (200,900)
Net Increase (Decrease) in Sales and Transfer Prices and Production Costs | 82,300 | 362,400 | (364,800)
Extensions Discoveries Less Related Costs | 226,300 | 130,500 | 70,500
Improved recovery, net of production costs | 0 | 0 | 0
Increase Due to Purchases of Minerals in Place | 9,500 | 99,800 | 0
Decrease Due to Sales of Minerals in Place | 0 | (500) | (1,100)
Changes in Estimated Future Development Costs | 51,100 | 34,100 | 43,600
Previously Estimated Development Costs Incurred During Period | 56,300 | 43,100 | 46,400
Accretion of Discount | 105,000 | 76,500 | 115,900
Changes in Future Income Tax Expense Estimates on Future Cash Flows Related to Proved Oil and Gas Reserves | (55,800) | (103,300) | 142,800
Revisions of Previous Quantity Estimates | (92,900) | (132,000) | (155,500)
Standardized Measure of Discounted Future Net Cash Flow of Proved Oil and Gas Reserves, Other | 2,400 | (3,300) | (7,900)
Standardized Measure of Discounted Future Net Cash Flow of Proved Oil and Gas Reserves, Period Increase (Decrease) | 82,700 | 237,300 | (311,000)
Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Ending Balance | $ 978,800 | $ 896,100 | $ 658,800

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- Definition The increase in the net discounted value of the proved oil and gas reserves due only to the passage of time. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 59BB -Subparagraph h -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 35 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=6821537&loc=d3e62500-109447 + Details
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- Definition The change in the discounted value of the proved oil and gas reserves due to financial transactions where new reserves were purchased. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 19 -Paragraph 59BB -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 35 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=6821537&loc=d3e62500-109447 + Details
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