Trading Activities - Gross Fair Values of Derivative Instruments of Futures and Forward Contracts as Separate Assets and Liabilities (Detail) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Futures Contracts [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	$ 1,503,294	$ 2,377,628
Total unrealized depreciation on open contracts	(1,005,209)	(639,577)
Net unrealized appreciation (depreciation) on open contracts	498,085	1,738,051
Futures Contracts [Member] | Commodity [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	913,269	1,273,423
Total unrealized depreciation on open contracts	(120,777)	(187,625)
Futures Contracts [Member] | Equity [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	74,944	489,126
Total unrealized depreciation on open contracts	(334,989)	(107,968)
Futures Contracts [Member] | Currencies [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	100,428	196,144
Total unrealized depreciation on open contracts	(94,561)	(3,001)
Futures Contracts [Member] | Interest Rates [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	414,653	418,935
Total unrealized depreciation on open contracts	(454,882)	(340,983)
Forward Contracts [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	483,676	1,275,513
Total unrealized depreciation on open contracts	(757,393)	(789,082)
Net unrealized appreciation (depreciation) on open contracts	(273,717)	486,431
Forward Contracts [Member] | Commodity [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	371,139	897,185
Total unrealized depreciation on open contracts	(576,574)	(385,217)
Forward Contracts [Member] | Currencies [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	112,537	378,328
Total unrealized depreciation on open contracts	$ (180,819)	$ (403,865)