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Fair Value of Financial Instruments (Fair Value of Derivative Instruments) (Details) (Commodity Contracts [Member], Futures [Member], Assets [Member], USD $)
Mar. 31, 2013
Dec. 31, 2012
Commodity Contracts [Member] | Futures [Member] | Assets [Member]
   
Derivatives, Fair Value [Line Items]    
Derivatives not Accounted for as Hedging Instruments $ 3,869,470 $ 1,556,910