Summary of Significant Accounting Policies - Fair Value of Derivative Instruments and Effect of Derivative Instruments on Statements of Income and Expenses (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Commodity Futures Contracts Assets	$ 0		$ 0		$ 0
Commodity Futures Contracts Liabilities	(23,171,081)		(23,171,081)		$ (13,474,175)
Net Realized Gain (Loss)	(2,094,540)	$ (2,039,502)	(16,420,885)	$ (14,707,548)
Net Change in Unrealized Gain (Loss)	(14,669,515)	22,763,005	(9,694,179)	19,951,855
Net realized and net change in unrealized gain (loss) on United States Treasury Obligations and Currency Futures Contracts	(16,764,055)	20,723,503	(26,115,064)	5,244,307
Commodity Contract [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net Realized Gain (Loss)	(2,095,499)	(2,041,000)	(16,422,029)	(14,709,256)
Net Change in Unrealized Gain (Loss)	(14,673,468)	22,767,125	(9,696,906)	19,954,375
Net realized and net change in unrealized gain (loss) on United States Treasury Obligations and Currency Futures Contracts	$ (16,768,967)	$ 20,726,125	$ (26,118,935)	$ 5,245,119