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Organization and Business (Additional Information) (Details) (USD $)	1 Months Ended
	Dec. 06, 2007	Dec. 04, 2007	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011	Feb. 29, 2012 Creation Baskets [Member]	Feb. 29, 2012 Prior to February 29, 2012 [Member] Creation Baskets [Member]	Mar. 31, 2013 Beginning on January 1, 2013 and after [Member]	Mar. 31, 2013 Open Cleared Swap and Futures Contracts [Member] Open Futures Contracts, Long [Member] United States [Member] Contract
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Number of Contracts										1,066
Number of units per basket							50,000	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
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		$ 41.03	$ 39.81	$ 45.81	$ 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			111,000,000