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Coal and Other Mineral Rights (Tables)
 12 Months Ended
Dec. 31, 2011
Coal and Other Mineral Rights [Abstract]  
Coal and other mineral rights
                 
    December 31,
2011		     December 31,
2010		  
    (In thousands)  

Coal and other mineral rights

   $ 1,645,451     $ 1,629,286  

Less accumulated depletion and amortization

     (387,950 )      (347,650 ) 
   

 

 

    

 

 

  

Net book value

   $ 1,257,501     $ 1,281,636  
   

 

 

    

 

 

  

 

                         
    For the years ended
December 31,		  
    2011     2010     2009  
    (In thousands)  

Total depletion and amortization expense on coal and other mineral interests

   $ 47,230     $ 38,501     $ 48,591