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Fair Value of Financial Instruments (Valuation of Securities Using Fair Value Hierarchy) (Details) (USD $)
Mar. 31, 2013
Dec. 31, 2012
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities, fair value $ 77,175,447 $ 92,755,785
Exchange-Traded Futures Contracts [Member] | United States [Member]
   
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities, fair value 3,869,470 1,556,910
Fair Value, Inputs, Level 1 [Member] | Short-Term Investments [Member]
   
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities, fair value 77,175,447 92,755,785
Fair Value, Inputs, Level 1 [Member] | Exchange-Traded Futures Contracts [Member] | United States [Member]
   
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities, fair value $ 3,869,470 $ 1,556,910