Net Loss per Common Share - Computation of Basic and Diluted Net Loss per Common 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
Basic and diluted net loss per common share:
Net loss	$ (19,135,612)	$ (13,762,214)	$ (10,640,376)	$ (8,281,974)	$ (8,280,916)	$ (4,805,559)	$ (43,538,202)	$ (21,368,449)
Weighted average common shares outstanding, basic and diluted	34,445,489			26,325,904			33,771,671	25,875,783
Net loss per common share, basic and diluted	$ (0.56)			$ (0.31)			$ (1.29)	$ (0.83)