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Organization and Business (Additional Information) (Details) (USD $)
 1 Months Ended 6 Months Ended
Dec. 06, 2007
Dec. 04, 2007
Unit
Jun. 30, 2013
Unit
Dec. 31, 2012
Jun. 30, 2012
Dec. 31, 2011
Feb. 29, 2012
Creation Baskets [Member]
Feb. 29, 2012
Redemption Baskets [Member]
Feb. 29, 2012
Prior to February 29, 2012 [Member]
Creation Baskets [Member]
Feb. 29, 2012
Prior to February 29, 2012 [Member]
Redemption Baskets [Member]
Jun. 30, 2013
From July 1, 2011 through December 31, 2013 [Member]
Jun. 30, 2013
From July 1, 2011 through December 31, 2013 [Member]
Redemption Baskets [Member]
Jun. 30, 2013
Open Cleared Swap and Futures Contracts [Member]
Open Futures Contracts, Long [Member]
United States [Member]
Contracts
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]                          
Number of Contracts                         772 [1]
Number of units per basket             50,000 50,000 100,000 100,000      
Fee paid by Authorized Purchasers for each order placed to create one or more Creation Baskets or to redeem one or more baskets                     1,000 350  
Number of initially registered units on Form S-1 with the U.S. Securities and Exchange Commission   11,000,000                      
Net asset value per unit $ 50.00   $ 40.07 $ 39.81 $ 37.90 $ 43.46              
Number of units issued 300,000                        
Value of units issued $ 15,000,000                        
Commenced investment operations date     Dec. 06, 2007                    
Number of registered units     100,000,000                    
[1] Collateral amounted to $6,076,684 on open futures contracts.