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Derivative Instruments and Risk Management (Details) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Carrying Amount [Member]
   
Summary of commodity swaps    
Commodity swaps $ 0.1 $ 0.2
Notional quantity- 2075 tonnes [Member] | Carrying Amount [Member]
   
Summary of commodity swaps    
Commodity swaps   0.2
Notional quantity- 2075 tonnes [Member] | Fair Value [Member]
   
Summary of commodity swaps    
Commodity swaps   0.2
Notional quantity- [525] tonnes [Member] | Carrying Amount [Member]
   
Summary of commodity swaps    
Commodity swaps 0.1  
Notional quantity- [525] tonnes [Member] | Fair Value [Member]
   
Summary of commodity swaps    
Commodity swaps $ 0.1