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FAIR VALUE OF FINANCIAL INSTRUMENTS (Valuation of Securities Using Fair Value Hierarchy) (Details) - USD ($) | Jun. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Short-Term Investments [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Securities, fair value | $ 311,184,062 | $ 483,194,474
Exchange-Traded Futures Contracts [Member] | United States Contracts [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Securities, fair value | (5,130,125) | 55,721,680
Fair Value, Inputs, Level 1 [Member] | Short-Term Investments [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Securities, fair value | 311,184,062 | 483,194,474
Fair Value, Inputs, Level 1 [Member] | Exchange-Traded Futures Contracts [Member] | United States Contracts [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Securities, fair value | (5,130,125) | 55,721,680
Fair Value, Inputs, Level 2 [Member] | Short-Term Investments [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Securities, fair value | 0 | 0
Fair Value, Inputs, Level 2 [Member] | Exchange-Traded Futures Contracts [Member] | United States Contracts [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Securities, fair value | 0 | 0
Fair Value, Inputs, Level 3 [Member] | Short-Term Investments [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Securities, fair value | 0 | 0
Fair Value, Inputs, Level 3 [Member] | Exchange-Traded Futures Contracts [Member] | United States Contracts [Member] |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |
Securities, fair value | $ 0 | $ 0

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- Definition Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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- 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. + References No definition available. + Details
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