Creation and Redemption of Creation Units - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016 $ / EquityUnit shares
Creation And Redemption Of Creation Units [Line Items]
Creation Unit, block Shares of a Fund	50,000
Fixed transaction fee per Creation Unit | $ / EquityUnit	500
Variable transaction fee, percent of the value of the Creation Unit, maximum	0.10%
Volatility Index Fund [Member]
Creation And Redemption Of Creation Units [Line Items]
Creation Unit, block Shares of a Fund	25,000
Variable transaction fee, percent of the value of the Creation Unit, maximum	0.05%