Organization - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2021 CreationUnit shares	Dec. 31, 2020 shares	Feb. 23, 2015 shares
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Purchase agreement transaction date	Feb. 23, 2015
General shares, shares issued	40	40	40
Ratio of the notional value of futures contracts	200.00%
Ratio of the notional value of futures contracts	166.00%
Treasury obligation measurement maximum maturity period	12 months
Number of shares issued per creation unit	100,000
Minimum number of Creation Units that can be purchased | CreationUnit	1