Net Loss per Common Share - Computation of Basic and Diluted Net Loss per Common Share (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Basic and diluted net loss per common share:
Net loss	$ (24,806,984)	$ (19,135,612)	$ (13,762,214)	$ (10,640,376)	$ (9,597,015)	$ (8,281,974)	$ (8,280,916)	$ (4,805,559)	$ (68,345,186)	$ (30,965,464)	$ (28,943,392)
Weighted average common shares outstanding, basic and diluted									34,020,257	26,883,656	22,764,606
Net loss per common share, basic and diluted	$ (0.71)	$ (0.56)	$ (0.41)	$ (0.32)	$ (0.32)	$ (0.31)	$ (0.32)	$ (0.19)	$ (2.01)	$ (1.15)	$ (1.27)