Derivative Instruments - Effect of Derivative Instruments on Statements of Income and Expenses (Detail) - Currency Futures Contract [Member] - Not Designated as Hedging Instrument [Member] - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Futures contracts, realized gain (loss)	$ (118,398)	$ 1,353,674
Futures contracts, unrealized gain (loss)	(531,434)	(695,415)
Net Realized and Net Change in Unrealized Gain (Loss) on United States Treasury Obligations, Affiliated Investments and Currency Futures Contracts	$ (649,832)	$ 658,259