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Asset Retirement Obligations
 12 Months Ended
Dec. 31, 2011
Asset Retirement Obligations [Abstract]  
Asset Retirement Obligations

9. Asset Retirement Obligations

The following table reflects the changes in the Company's ARO during the years ended December 31, 2011 and 2010:

September 30, September 30,
       December 31,  
       2011      2010  
       (In thousands)  

Asset retirement obligation — beginning of period

      $ 7,640       $ 6,511   

Liabilities incurred during period

        4,100         1,747   

Liabilities settled during period

        (369 )       (422 ) 

Accretion expense during period

        590         414   

Revisions to estimates

        1,114         (610 ) 
    

 

 

     

 

 

  

Asset retirement obligation — end of period

      $ 13,075       $ 7,640