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, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net loss	$ (4,797,270)	$ (5,370,846)	$ (4,102,729)	$ (5,379,947)	$ (10,168,116)	$ (9,482,676)
Denominator:
Weighted-average shares outstanding-basic and diluted	28,657,384		28,375,379		28,629,189	26,549,895
Net loss per share, basic and diluted	$ (0.17)		$ (0.14)		$ (0.36)	$ (0.36)