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Contracts and Agreements (Brokerage Commissions) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Long Duration Contracts Assumptions By Product And Guarantee [Line Items]
Brokerage commissions	$ 8,669	$ 6,437
Brokerage commissions as a percentage of average daily net assets	0.04%	0.04%
Rebalancing Investments Transaction [Member]
Long Duration Contracts Assumptions By Product And Guarantee [Line Items]
Brokerage commissions	$ 1,280	$ 4,323
Brokerage commissions as a percentage of average daily net assets	14.77%	67.16%
Trades Necessitated By Creation And Redemption Activity [Member]
Long Duration Contracts Assumptions By Product And Guarantee [Line Items]
Brokerage commissions	$ 7,389	$ 2,114
Brokerage commissions as a percentage of average daily net assets	85.23%	32.84%

X

- Definition

The amount of expense during the period for floor brokerage fees paid to other broker-dealers to execute trades on their behalf, stock exchange fees, order flow fees, and clearance fees.

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X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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X

- Definition

Percentage of Average Daily Net Assets

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