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Significant Accounting Policies (Detail) (USD $)
 3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Dec. 31, 2011
Annualized Rate Of Sponsors Fee     0.39%    
Sponsor Fees (in Dollars) $ 1,722,879 $ 1,311,536 $ 3,501,060 $ 2,453,158  
Accounts Payable, Related Parties, Current (in Dollars) $ 564,731   $ 564,731   $ 560,620 [1]
[1] Derived from audited Statement of Financial Condition as of December 31, 2011.