Derivative Instruments - Effect of Derivative Instruments on Statements of Income and Expenses (Detail) - Currency Futures Contracts [Member] - Not Designated as Hedging Instrument [Member] - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Futures contracts, realized gain (loss)	$ 29,619,708	$ (51,958,105)	$ 38,971,461
Futures contracts, unrealized gain (loss)	3,438,120	(9,961,447)	(7,087,803)
Net Realized and Net Change in Unrealized Gain (Loss) on United States Treasury Obligations, Affiliated Investments and Currency Futures Contracts	$ 33,057,828	$ (61,919,552)	$ 31,883,658