Service Providers and Related Party Agreements - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Related Party Transaction [Line Items]
Managing owner waived fees	$ 25,887	$ 23,040	$ 52,611	$ 48,848
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