Summary of Significant Accounting Policies - Summary of the Tiered Valuation Input Levels (Detail) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
United States Treasury Obligations	$ 217,001,291	$ 236,994,724
Commodity Futures Contracts	(23,171,081)	(13,474,175)
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
United States Treasury Obligations		236,994,724
Commodity Futures Contracts	(23,171,081)
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
United States Treasury Obligations	$ 217,001,291
Commodity Futures Contracts		$ (13,474,175)

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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- Definition

The fair value as of the balance sheet date of firm holdings in debt obligations issued by the US government including short-term Treasury bills, medium-term Treasury notes, and long-term Treasury bonds, as well as debt issued by agencies. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 940

-SubTopic 320

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969

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- Definition

This element represents the net excess or deficiency of the fair value of an investment (security, contract) over or under its cost (face amount, notional amount), respectively, which excess value or deficiency has not been recognized in earnings of the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 946

-SubTopic 320

-Section S99

-Paragraph 22

-URI http://asc.fasb.org/extlink&oid=34726532&loc=SL6090603-123010

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