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Contracts and Agreements (Brokerage Commissions) (Details) - USD ($) | 3 Months Ended
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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%

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- 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. + References No definition available. + Details
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