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Significant Accounting Policies (Narrative) (Details) - USD ($)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Significant Accounting Policies [Abstract]        
Reserve for uncertain tax positions $ 0      
Expense ratio [1] 0.60% 0.60%    
Sponsor Fees $ 3,123,275 $ 4,376,182 $ 4,973,343 $ 4,973,343
Fees payable to Sponsor 205,938 320,608    
All other expenses $ 0 $ 0 $ 0  
[1] Effective January 1, 2014, the Trust has adopted the provisions of Topic 946. Refer to Note 2.1 for additional information.