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Significant Accounting Policies (Narrative) (Details) (USD $)
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Dec. 31, 2012
Significant Accounting Policies [Abstract]          
Annualized rate of sponsors fee     0.39%    
Sponsor fees $ 1,446,581 $ 1,722,879 $ 3,258,496 $ 3,501,060  
Fees payable to the Sponsor $ 386,611   $ 386,611   $ 630,835