Net Loss per Share - Numerator and Denominator Used in Computing Basic and Diluted Net Loss per Share (Details) - USD ($)	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net loss	$ (4,740,232)	$ (4,797,270)	$ (5,370,846)	$ (4,843,408)	$ (4,102,729)	$ (5,379,947)	$ (14,908,348)	$ (14,326,084)
Denominator:
Weighted-average shares outstanding-basic and diluted	31,367,044			28,434,406			29,551,836	27,184,968
Net loss per share, basic and diluted	$ (0.15)			$ (0.17)			$ (0.50)	$ (0.53)