Condensed Consolidated Statements of Comprehensive Loss (unaudited) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (30,819,866)	$ (17,675,373)	$ (77,785,576)	$ (49,244,511)
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities	(584,317)	(103,505)	972,231	414,368
Comprehensive loss	$ (31,404,183)	$ (17,778,878)	$ (76,813,345)	$ (48,830,143)