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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net loss	$ (5,380,846)	$ (6,488,442)	$ (17,038,022)	$ (20,366,469)
Denominator:
Weighted-average shares outstanding-basic and diluted	11,603,617	7,053,010	9,794,651	6,985,924
Net loss per share, basic and diluted	$ (0.46)	$ (0.92)	$ (1.74)	$ (2.92)