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Fair Value Measurements - Reconciliation of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis using Significant Unobservable Inputs (Parenthetical) (Details) | 12 Months Ended
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Dec. 31, 2012 | Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract] |  |
Fair value, level 3 transfers out description | During the years ended December 31, 2012 and 2010, the Company did not have any transfers between Level 1, Level 2 or Level 3 fair value measurements. | Fair values related to the Company’s oil and natural gas fixed price swaps, natural gas collars and interest rate swap were transferred from Level 3 to Level 2 in the fourth quarter of 2011 due to enhancements to the Company’s internal valuation process, including the use of observable inputs to assess the fair value.

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- Definition Disclosures concerning the reasons for transfers out of Level 3 of the fair value hierarchy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258 + Details
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