Annual report pursuant to Section 13 and 15(d)

Financial Instruments - Derivatives Gross Presentation on Condsolidated Balance Sheet (Details)

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Financial Instruments - Derivatives Gross Presentation on Condsolidated Balance Sheet (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Commodity Contract [Member]
   
Derivative [Line Items]    
Derivative Assets $ 613 $ 2,310
Derivative Liabilities 474 1,774
Designated as Hedging Instrument [Member] | Interest Rate Contract [Member]
   
Derivative [Line Items]    
Derivative Assets   0
Designated as Hedging Instrument [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Contract [Member]
   
Derivative [Line Items]    
Derivative Liabilities   0
Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member]
   
Derivative [Line Items]    
Derivative Assets   0
Derivative Liabilities   0
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
   
Derivative [Line Items]    
Derivative Assets 17,512  
Interest Rate Contract [Member] | Designated as Hedging Instrument [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
   
Derivative [Line Items]    
Derivative Liabilities 38,729  
Interest Rate Contract [Member] | Not Designated as Hedging Instrument [Member]
   
Derivative [Line Items]    
Derivative Assets 4,283  
Derivative Liabilities $ 9,491