Trading Activities - Gross Fair Values of Derivative Instruments of Futures and Option Contracts, as Separate Assets and Liabilities (Detail)	Dec. 31, 2018 USD ($)
Derivative [Line Items]
Total options purchased	$ 305,214
Total options written	(409,571)
Forwards [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	2,203,511
Total unrealized depreciation on open contracts	(2,567,628)
Net unrealized appreciation (depreciation) on open contracts	(364,117)
Energy [Member]
Derivative [Line Items]
Total options purchased	35,640
Total options written	(34,760)
Grains [Member]
Derivative [Line Items]
Total options purchased	27,500
Livestock [Member]
Derivative [Line Items]
Total options purchased	19,620
Total options written	(17,820)
Metals [Member]
Derivative [Line Items]
Total options purchased	222,454
Total options written	(239,069)
Metals [Member] | Forwards [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	2,203,511
Total unrealized depreciation on open contracts	(2,567,628)
Softs [Member]
Derivative [Line Items]
Total options written	(117,922)
Futures [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	6,579,887
Total unrealized depreciation on open contracts	(4,822,376)
Net unrealized appreciation (depreciation) on open contracts	1,757,511
Futures [Member] | Currencies [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	14,578
Total unrealized depreciation on open contracts	(1,159)
Futures [Member] | Energy [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	5,628,038
Total unrealized depreciation on open contracts	(3,938,643)
Futures [Member] | Grains [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	157,540
Total unrealized depreciation on open contracts	(66,943)
Futures [Member] | Livestock [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	317,100
Total unrealized depreciation on open contracts	(252,835)
Futures [Member] | Metals [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	125,934
Total unrealized depreciation on open contracts	(295,124)
Futures [Member] | Softs [Member]
Derivative [Line Items]
Total unrealized appreciation on open contracts	336,697
Total unrealized depreciation on open contracts	$ (267,672)