Trading Activities - Gross Fair Values of Derivative Instruments of Option Contracts as Separate Assets and Liabilities (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Options Purchased Indices [Member]
Assets
Total options purchased	$ 211,200	$ 621,000
Options Purchased [Member]
Assets
Total options purchased	211,200	621,000
Written Options Indices [Member]
Liabilities
Total written options	(209,000)	(699,200)
Written Options [Member]
Liabilities
Total written options	$ (209,000)	$ (699,200)