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CONTRACTS AND AGREEMENTS (Brokerage Commissions) (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Long Duration Contracts Assumptions By Product And Guarantee [Line Items] |  |  |
Brokerage commissions | $ 17,897 | $ 22,207 | $ 19,025
Brokerage commissions as a percentage of average daily net assets | 0.02% | 0.02% | 0.03%
Rebalancing Investments Transaction [Member] |  |  |
Long Duration Contracts Assumptions By Product And Guarantee [Line Items] |  |  |
Brokerage commissions | $ 13,735 | $ 17,872 | $ 11,997
Brokerage commissions as a percentage of average daily net assets | 76.74% | 80.48% | 63.06%
Trades Necessitated By Creation And Redemption Activity [Member] |  |  |
Long Duration Contracts Assumptions By Product And Guarantee [Line Items] |  |  |
Brokerage commissions | $ 4,162 | $ 4,335 | $ 7,028
Brokerage commissions as a percentage of average daily net assets | 23.26% | 19.52% | 36.94%

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