Summarizes activity of Level 3 inputs measured on a recurring basis (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Beginning Balance	$ 5,338,886	$ 2,088,889
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Purchases		1,527,776
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Period Increase (Decrease)	(44,886)	1,722,221
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers, Net	5,294,000
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers out of Level 3	(5,294,000)
Ending Balance	$ 0	$ 5,338,886