Trading Activities - Gross Fair Values of Derivative Instruments of Futures and Forward Contracts as Separate Assets and Liabilities (Detail) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Futures Contracts [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	$ 1,531,065	$ 2,377,628
Total unrealized depreciation on open contracts	(731,733)	(639,577)
Net unrealized appreciation (depreciation) on open contracts	799,332	1,738,051
Futures Contracts [Member] | Commodity [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	788,766	1,273,423
Total unrealized depreciation on open contracts	(105,784)	(187,625)
Futures Contracts [Member] | Equity [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	106,764	489,126
Total unrealized depreciation on open contracts	(450,822)	(107,968)
Futures Contracts [Member] | Currencies [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	283,873	196,144
Total unrealized depreciation on open contracts	(39,245)	(3,001)
Futures Contracts [Member] | Interest Rates [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	351,662	418,935
Total unrealized depreciation on open contracts	(135,882)	(340,983)
Forward Contracts [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	726,521	1,275,513
Total unrealized depreciation on open contracts	(1,033,278)	(789,082)
Net unrealized appreciation (depreciation) on open contracts	(306,757)	486,431
Forward Contracts [Member] | Commodity [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	452,379	897,185
Total unrealized depreciation on open contracts	(892,877)	(385,217)
Forward Contracts [Member] | Currencies [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	274,142	378,328
Total unrealized depreciation on open contracts	$ (140,401)	$ (403,865)