Summary of Significant Accounting Policies - Summary of Gross and Net Amounts of Offsetting Assets (Detail) - Commodity Futures Contract [Member] - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Offsetting Assets And Liabilities [Line Items]
Gross Amounts of Recognized Assets	$ 168,313,826	$ 355,260,235
Gross Amounts Offset Assets in the Statement of Financial Condition	(151,257,853)	(338,594,323)
Net Amounts of Assets Presented in the Statement of Financial Condition	17,055,973	16,665,912
Assets Net Amount	17,055,973	16,665,912
Gross Amounts of Recognized Liabilities	(151,257,853)	(373,040,379)
Gross Amounts Offset Liabilities in the Statement of Financial Condition	$ 151,257,853	338,594,323
Net Amounts of Liabilities Presented in the Statement of Financial Condition		(34,446,056)
Gross Amounts Not Offset in the Statement of Financial Condition - Financial Instruments Liabilities		$ 34,446,056