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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)				9 Months Ended
	Sep. 30, 2012	Feb. 29, 2012 Redemption Baskets	Feb. 29, 2012 Prior to February 29, 2012 Redemption Baskets	Sep. 30, 2012 Maximum
Significant Accounting Policies [Line Items]
Basis points subtracted from overnight Federal Funds Rate	0.32%
Minimum likelihood of tax benefits being recognized upon ultimate settlement	50.00%
Number of units per basket		$ 50,000	$ 100,000
Cash equivalents maturity period				6 months

X

- Definition

Cash Equivalents, Maturity Period

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- Definition

Market yields, basis point

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- Definition

Number of Units per Basket

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- Definition

Percentage Of Income Tax Examination Minimum Likelihood of Tax Benefits Being Realized Upon Settlement

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