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Standby Letters of Credit (Tables)
9 Months Ended
Sep. 30, 2011
Standby Letters of Credit [Abstract] 
Standby Letters of Credit
         
 
    September 30  
in thousands   2011  
 
     
Standby Letters of Credit
       
Risk management requirement for insurance claims
    $41,083  
Payment surety required by utilities
    133  
Contractual reclamation/restoration requirements
    8,482  
Financial requirement for industrial revenue bond
    14,230  
 
     
Total
    $63,928