Derivative Instruments - Effect of Derivative Instruments on Statements of Income and Expenses (Detail) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Futures contracts, realized gain (loss)	$ (19,382,968)	$ 15,257,206	$ (1,374,992)	$ 34,000,631
Futures contracts, unrealized gain (loss)	196,505	12,769,475	(51,262,745)	16,881,325
Net Realized and Net Change in Unrealized Gain (Loss) on United States Treasury Obligations, Affiliated Investments and Commodity Futures Contracts	(19,347,778)	28,062,349	(52,636,174)	50,966,624
Commodity Futures Contract [Member] \| Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Futures contracts, realized gain (loss)	(19,382,968)	15,257,206	(1,374,992)	34,000,631
Futures contracts, unrealized gain (loss)	196,505	12,769,475	(51,262,745)	16,881,325
Net Realized and Net Change in Unrealized Gain (Loss) on United States Treasury Obligations, Affiliated Investments and Commodity Futures Contracts	$ (19,186,463)	$ 28,026,681	$ (52,637,737)	$ 50,881,956

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.

No definition available.

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Amount of realized and unrealized gain (loss) on investment.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 10
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-Publisher FASB
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-Subparagraph (SX 210.5-03.7(c),9(a))
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-Publisher FASB
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-Topic 230
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The difference between the book value and the sale price of agreements to purchase or sell mineral resources, energy, and agricultural products at some future point. This element refers to the gain (loss) included in earnings and not to the cash proceeds.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 230
-SubTopic 10
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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of open agreements to purchase or sell mineral resources, energy, and agricultural products at some future point held at each balance sheet date, that was included in earnings for the period.

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