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Asset Retirement Obligation (Details) (USD $)
9 Months Ended
Sep. 30, 2014
Dec. 31, 2013
Asset Retirement Obligation    
Balance at beginning of period $ 75,853,000  
Liabilities incurred 4,360,000  
Liabilities settled (411,000)  
Liabilities divested (899,000)  
Change in estimate 33,810,000  
Accretion expense 3,528,000  
Balance at end of period 116,241,000  
Current portion of asset retirement obligation $ 2,000,000 $ 2,000,000