Derivative Instruments - Effect of Derivative Instruments on Statements of Income and Expenses (Detail) - Currency Futures Contracts [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)	$ (933,778)	$ (18,719,768)
Futures contracts, unrealized gain (loss)	7,045,633	10,270,835
Net Realized and Net Change in Unrealized Gain (Loss) on United States Treasury Obligations, Affiliated Investments and Currency Futures Contracts	$ 6,111,855	$ (8,448,933)