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Significant Accounting Policies (Narrative) (Details) (USD $)
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dec. 31, 2012
Significant Accounting Policies [Abstract]      
Annualized rate of sponsors fee 0.39%    
Sponsor fees $ 1,811,915 $ 1,778,181  
Fees payable to the Sponsor $ 610,274   $ 630,835