Net Loss Per Share - Schedule of Basic and Diluted Net Loss Per Share (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net Loss Per Share [Line Items]
Net loss	$ (13,800,195)	$ (13,182,758)
Common Stock [Member]
Net Loss Per Share [Line Items]
Net loss	$ (13,800,195)
Weighted average number of shares outstanding during the period	30,329,640	24,609,050
Basic and diluted net loss per share	$ (0.46)	$ (0.54)