Net Loss per Share - Numerator and Denominator Used in Computing Basic and Diluted Net Loss per Share (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net loss	$ (4,102,729)	$ (5,840,902)	$ (9,482,676)	$ (11,657,176)
Denominator:
Weighted-average shares outstanding-basic and diluted	28,375,379	9,769,322	26,549,895	8,875,177
Net loss per share, basic and diluted	$ (0.14)	$ (0.60)	$ (0.36)	$ (1.31)