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Asset Retirement Obligations (Tables)
6 Months Ended
Jun. 30, 2012
Asset Retirement Obligations [Abstract]  
Changes in the Company's asset retirement obligations
         

Beginning asset retirement obligations

  $ 4,269  

Liabilities incurred during period

    326  

Liabilities settled during period

    —    

Accretion expense

    111  
   

 

 

 

Ending asset retirement obligations

  $ 4,706