Service Providers and Related Party Agreements - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Managing owner waived fees	$ 114,990	$ 88,610	$ 25,204
Compensation for service from advisors	$ 0
The Managing Owner [Member]
Related Party Transaction [Line Items]
Management fee percentage per annum of daily NAV	0.75%
Fee waiver termination notice period	60 days