Summary of Significant Accounting Policies - Effect of Derivative Instruments on Statements of Income and Expenses (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Futures contracts, realized gain (loss)	$ 38,971,461	$ 79,589,339	$ 79,130,173
Futures contracts, unrealized gain (loss)	(7,087,803)	(10,493,639)	20,149,887
Net Realized and Net Change in Unrealized Gain (Loss) on United States Treasury Obligations and Currency Futures Contracts	31,827,335	69,094,297	99,306,513
Currency Futures Contracts [Member] | Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Futures contracts, realized gain (loss)	38,971,461	79,589,339	79,130,173
Futures contracts, unrealized gain (loss)	(7,087,803)	(10,493,639)	20,149,887
Net Realized and Net Change in Unrealized Gain (Loss) on United States Treasury Obligations and Currency Futures Contracts	$ 31,883,658	$ 69,095,700	$ 99,280,060