Trading Activities - Gross Fair Values of Derivative Instruments of Futures and Forward Contracts as Separate Assets and Liabilities (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Futures Contracts [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	$ 1,456,716	$ 2,377,628
Total unrealized depreciation on open contracts	(1,122,513)	(639,577)
Net unrealized appreciation (depreciation) on open contracts	334,203	1,738,051
Futures Contracts [Member] | Commodity [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	508,863	1,273,423
Total unrealized depreciation on open contracts	(389,356)	(187,625)
Futures Contracts [Member] | Equity [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	248,473	489,126
Total unrealized depreciation on open contracts	(229,595)	(107,968)
Futures Contracts [Member] | Currencies [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	241,791	196,144
Total unrealized depreciation on open contracts	(78,105)	(3,001)
Futures Contracts [Member] | Interest Rates [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	457,589	418,935
Total unrealized depreciation on open contracts	(425,457)	(340,983)
Forward Contracts [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	623,038	1,275,513
Total unrealized depreciation on open contracts	(632,108)	(789,082)
Net unrealized appreciation (depreciation) on open contracts	(9,070)	486,431
Forward Contracts [Member] | Commodity [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	374,564	897,185
Total unrealized depreciation on open contracts	(230,751)	(385,217)
Forward Contracts [Member] | Currencies [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	248,474	378,328
Total unrealized depreciation on open contracts	$ (401,357)	$ (403,865)