Additional Valuation Information - Summary of the Tiered Valuation Input Levels (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
United States Treasury Obligations	$ 1,839,039,728	$ 2,403,838,023
Exchange-Traded Fund	249,742,548
Money Market Mutual Fund	68,003,679	131,029,805
Total Investments in Securities	2,156,785,955	2,534,867,828
Commodity Futures Contracts, Appreciation	141,995,427
Commodity Futures Contracts, Depreciation	(26,326,112)
Commodity Futures Contracts	115,669,315	101,032,417
Total Investments	2,272,455,270	2,635,900,245
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Exchange-Traded Fund	249,742,548
Money Market Mutual Fund	68,003,679	131,029,805
Total Investments in Securities	317,746,227	131,029,805
Commodity Futures Contracts, Appreciation	141,995,427
Commodity Futures Contracts, Depreciation	(26,326,112)
Commodity Futures Contracts	115,669,315	101,032,417
Total Investments	433,415,542	232,062,222
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
United States Treasury Obligations	1,839,039,728	2,403,838,023
Total Investments in Securities	1,839,039,728	2,403,838,023
Total Investments	$ 1,839,039,728	$ 2,403,838,023