Net Loss per Share - Numerator and Denominator Used in Computing Basic and Diluted Net Loss per Share (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net loss	$ (4,843,408)	$ (5,380,846)	$ (14,326,084)	$ (17,038,022)
Denominator:
Weighted-average shares outstanding-basic and diluted	28,434,406	11,603,617	27,184,968	9,794,651
Net loss per share, basic and diluted	$ (0.17)	$ (0.46)	$ (0.53)	$ (1.74)