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Significant Accounting Policies (Narrative) (Details) (USD $)
3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Dec. 31, 2012
Significant Accounting Policies [Abstract]          
Annualized rate of sponsors fee     0.39%    
Sponsor fees $ 1,300,748 $ 1,802,987 $ 4,559,244 $ 5,304,047  
Fees payable to the Sponsor $ 407,095   $ 407,095   $ 630,835