Organization - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2020 CreationUnit shares	Dec. 31, 2019 shares	Feb. 23, 2015 shares	Aug. 03, 2006 Trust
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of series of trusts | Trust				7
Purchase agreement transaction date	Feb. 23, 2015
General shares, shares issued	40	40	40
Treasury obligation measurement maximum maturity period	12 months
Minimum number of Creation Units that can be purchased | CreationUnit	1
Number of shares issued per Creation Unit	200,000