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Risk Concentrations Risk Concentrations (Narrative) (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2012
T
Dec. 31, 2011
Dec. 31, 2010
Concentration Risk [Line Items]      
Sales to customers in foreign countries $ 1,200,000 $ 920,000 $ 471,500
Tons of coal sold 140,800,000    
Receivables 332,080 469,179  
Trade accounts receivable 247,539 380,595  
Percentage of tons sold under long term contract 70.00%    
Long term contracts percentage of company revenue 50.00%    
Long-term contracts, life term, minimum 1 year    
Long-term contracts, life term, maximum 8 years    
Electric Utilities [Member]
     
Concentration Risk [Line Items]      
Receivables 159,500 261,200  
Percentage of total trade accounts receivable 65.00% 69.00%  
Domestic And Foreign Steel Producers [Member]
     
Concentration Risk [Line Items]      
Trade accounts receivable $ 86,600 $ 117,400  
Trade receivables, percentage 35.00% 31.00%