Trading Activities - Gross Fair Values of Derivative Instruments of Futures and Forward Contracts as Separate Assets and Liabilities (Detail) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Futures Contracts [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	$ 3,195,935	$ 2,377,628
Total unrealized depreciation on open contracts	(663,783)	(639,577)
Net unrealized appreciation (depreciation) on open contracts	2,532,152	1,738,051
Futures Contracts [Member] | Commodity [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	1,484,033	1,273,423
Total unrealized depreciation on open contracts	(33,064)	(187,625)
Futures Contracts [Member] | Equity [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	960,553	489,126
Total unrealized depreciation on open contracts	(166,623)	(107,968)
Futures Contracts [Member] | Currencies [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	104,757	196,144
Total unrealized depreciation on open contracts	(155,450)	(3,001)
Futures Contracts [Member] | Interest Rates [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	646,592	418,935
Total unrealized depreciation on open contracts	(308,646)	(340,983)
Forward Contracts [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	394,721	1,275,513
Total unrealized depreciation on open contracts	(538,303)	(789,082)
Net unrealized appreciation (depreciation) on open contracts	(143,582)	486,431
Forward Contracts [Member] | Commodity [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	97,294	897,185
Total unrealized depreciation on open contracts	(201,333)	(385,217)
Forward Contracts [Member] | Currencies [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	297,427	378,328
Total unrealized depreciation on open contracts	$ (336,970)	$ (403,865)