Organization - Additional Information (Detail)		9 Months Ended
	Feb. 23, 2015 USD ($) shares	Sep. 30, 2017 Basket shares	Dec. 31, 2016 shares
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Partners' capital contribution | $	$ 1,000
General shares, shares issued	40	40	40
Treasury obligation measurment maximum maturity period		12 months
Minimum number of Baskets that can be purchased | Basket		1
Number of shares issued per basket		200,000