Trading Activities - Offsetting of Derivative Assets and Liabilities (Detail) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Gross Amounts Recognized, Assets	$ 3,590,656	$ 3,653,141
Gross Amounts Offset in the Statements of Financial Condition, Assets	(1,058,504)	(1,428,659)
Amounts Presented in the Statements of Financial Condition, Assets	2,532,152	2,224,482
Gross Amounts Not Offset in the Statements of Financial Condition, Financial Instruments, Assets	0	0
Gross Amounts Not Offset in the Statements of Financial Condition, Cash Collateral Received/ Pledged, Assets	0	0
Net Amount, Assets	2,532,152	2,224,482
Gross Amounts Recognized, Liabilities	(1,202,086)	(1,428,659)
Gross Amounts Offset in the Statements of Financial Condition, Liabilities	1,058,504	1,428,659
Amounts Presented in the Statements of Financial Condition, Liabilities	(143,582)
Gross Amounts Not Offset in the Statements of Financial Condition, Financial Instruments, Liabilities	0	0
Gross Amounts Not Offset in the Statements of Financial Condition, Cash Collateral Received/ Pledged, Liabilities	0	0
Net Amount, Liabilities	(143,582)
Net fair value	2,388,570	2,224,482
Futures Contracts [Member]
Derivative [Line Items]
Gross Amounts Recognized, Assets	3,195,935	2,377,628
Gross Amounts Offset in the Statements of Financial Condition, Assets	(663,783)	(639,577)
Amounts Presented in the Statements of Financial Condition, Assets	2,532,152	1,738,051
Gross Amounts Not Offset in the Statements of Financial Condition, Financial Instruments, Assets	0	0
Gross Amounts Not Offset in the Statements of Financial Condition, Cash Collateral Received/ Pledged, Assets	0	0
Net Amount, Assets	2,532,152	1,738,051
Gross Amounts Recognized, Liabilities	(663,783)	(639,577)
Gross Amounts Offset in the Statements of Financial Condition, Liabilities	663,783	639,577
Gross Amounts Not Offset in the Statements of Financial Condition, Financial Instruments, Liabilities	0	0
Gross Amounts Not Offset in the Statements of Financial Condition, Cash Collateral Received/ Pledged, Liabilities	0	0
Forward Contracts [Member]
Derivative [Line Items]
Gross Amounts Recognized, Assets	394,721	1,275,513
Gross Amounts Offset in the Statements of Financial Condition, Assets	(394,721)	(789,082)
Amounts Presented in the Statements of Financial Condition, Assets		486,431
Gross Amounts Not Offset in the Statements of Financial Condition, Financial Instruments, Assets	0	0
Gross Amounts Not Offset in the Statements of Financial Condition, Cash Collateral Received/ Pledged, Assets	0	0
Net Amount, Assets		486,431
Gross Amounts Recognized, Liabilities	(538,303)	(789,082)
Gross Amounts Offset in the Statements of Financial Condition, Liabilities	394,721	789,082
Amounts Presented in the Statements of Financial Condition, Liabilities	(143,582)
Gross Amounts Not Offset in the Statements of Financial Condition, Financial Instruments, Liabilities	0	0
Gross Amounts Not Offset in the Statements of Financial Condition, Cash Collateral Received/ Pledged, Liabilities	0	$ 0
Net Amount, Liabilities	$ (143,582)