Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE OF FINANCIAL INSTRUMENTS (Narrative) (Details)

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FAIR VALUE OF FINANCIAL INSTRUMENTS (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
9 Months Ended 12 Months Ended
Sep. 30, 2013
Dec. 31, 2012
Dec. 31, 2002
Fair Value, Assets And Liabilities Components [Line Items]      
Management Estimate of 62% Fe 62.00%    
Supply agreement, customer receivable, basis spread on variable rate 3.50%    
Empire [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Loans Receivable, Fair Value Disclosure $ 14.3 $ 21.3  
Estimated credit-adjusted risk-free interest rate 1.98% 2.85%  
Accounts, Notes, Loans and Financing Receivable, Net, Noncurrent 13.4 19.3 120.0
Prior [Member] | Empire [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners     46.70%
Current [Member] | Empire [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Percent ownership interest after transaction     79.00%
Other Current Assets [Member] | Empire [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Other current assets 10.0 10.0  
Customer Supplemental Payments [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Maximum deferred portion of supplemental payments 22.3    
Supply agreement, customer receivable, stated interest rate 9.00%    
Supply agreement, customer receivable, description of variable rate basis prime rate    
Payments for (Proceeds from) Loans Receivable 22.3    
Loans Receivable, Fair Value Disclosure   21.3  
Estimated credit-adjusted risk-free interest rate   2.81%  
Customer Supplemental Payments [Member] | Other Current Assets [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Other current assets   22.3  
Amapa [Member]
     
Fair Value, Assets And Liabilities Components [Line Items]      
Equity Method Investments, Fair Value Disclosure 0 72.5  
Equity Method Investment, Other than Temporary Impairment $ 67.6 $ 365.4