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Asset Retirement Obligation (Details) (USD $)
3 Months Ended
Mar. 31, 2014
Asset Retirement Obligation  
Balance at the beginning of the period $ 75,853,000
Liabilities incurred 1,647,000
Liabilities divested (899,000)
Accretion expense 1,003,000
Balance at the end of the period 77,604,000
Asset retirement obligation, current $ 2,000,000