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, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Basic and diluted net loss per common share:
Net loss	$ (29,164,647)	$ (22,924,815)	$ (18,326,992)	$ (32,484,146)	$ (24,806,984)	$ (19,135,612)	$ (13,762,214)	$ (10,640,376)	$ (102,900,600)	$ (68,345,186)	$ (30,965,464)
Weighted average common shares outstanding, basic and diluted									37,206,928	34,020,257	26,883,656
Net loss per common share, basic and diluted	$ (0.79)	$ (0.61)	$ (0.49)	$ (0.88)	$ (0.71)	$ (0.56)	$ (0.41)	$ (0.32)	$ (2.77)	$ (2.01)	$ (1.15)