Condensed Consolidated Statements of Changes in Stockholders' Equity (unaudited) - USD ($)	Total	At-the-Market Offering	Common Shares	Common Shares At-the-Market Offering	Accumulated Deficit	Additional Paid-in Capital	Additional Paid-in Capital At-the-Market Offering	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2018	$ 136,666,983		$ 31,236		$ (302,264,619)	$ 439,118,089		$ (217,723)
Balance, Shares at Dec. 31, 2018			31,235,458
Stock-based compensation	15,091,269					15,091,269
Issuance of common stock, net of offering costs	29,454,033		$ 1,346			29,452,687
Issuance of common stock, net of offering costs, Shares			1,346,313
Net loss	(49,244,511)				(49,244,511)
Restricted stock vesting			$ 383			(383)
Restricted stock vesting, Shares			383,695
Exercise of stock options	1,777,456		$ 111			1,777,345
Exercise of stock options, Shares			111,091
Unrealized gain (loss) on available-for-sale securities	414,368							414,368
Balance at Sep. 30, 2019	134,159,598		$ 33,076		(351,509,130)	485,439,007		196,645
Balance, Shares at Sep. 30, 2019			33,076,557
Balance at Jun. 30, 2019	116,505,261		$ 31,524		(333,833,757)	450,007,344		300,150
Balance, Shares at Jun. 30, 2019			31,523,474
Stock-based compensation	4,601,214					4,601,214
Issuance of common stock, net of offering costs	29,454,033		$ 1,346			29,452,687
Issuance of common stock, net of offering costs, Shares			1,346,313
Net loss	(17,675,373)				(17,675,373)
Restricted stock vesting			$ 120			(120)
Restricted stock vesting, Shares			120,647
Exercise of stock options	1,377,968		$ 86			1,377,882
Exercise of stock options, Shares			86,123
Unrealized gain (loss) on available-for-sale securities	(103,505)							(103,505)
Balance at Sep. 30, 2019	134,159,598		$ 33,076		(351,509,130)	485,439,007		196,645
Balance, Shares at Sep. 30, 2019			33,076,557
Balance at Dec. 31, 2019	226,686,281		$ 38,461		(372,556,846)	599,097,090		107,576
Balance, Shares at Dec. 31, 2019			38,461,353
Stock-based compensation	22,121,591					22,121,591
Issuance of common stock, net of offering costs		$ 29,918,502		$ 1,163			$ 29,917,339
Issuance of common stock, net of offering costs, Shares				1,163,074
Net loss	(77,785,576)				(77,785,576)
Restricted stock vesting			$ 295			(295)
Restricted stock vesting, Shares			295,065
Exercise of stock options	3,206,938		$ 177			3,206,761
Exercise of stock options, Shares			176,509
Unrealized gain (loss) on available-for-sale securities	972,231							972,231
Balance at Sep. 30, 2020	205,119,967		$ 40,096		(450,342,422)	654,342,486		1,079,807
Balance, Shares at Sep. 30, 2020			40,096,001
Balance at Jun. 30, 2020	197,781,424		$ 38,825		(419,522,556)	615,601,031		1,664,124
Balance, Shares at Jun. 30, 2020			38,825,190
Stock-based compensation	8,246,921					8,246,921
Issuance of common stock, net of offering costs		$ 29,918,502		$ 1,163			$ 29,917,339
Issuance of common stock, net of offering costs, Shares				1,163,074
Net loss	(30,819,866)				(30,819,866)
Restricted stock vesting			$ 82			(82)
Restricted stock vesting, Shares			82,156
Exercise of stock options	577,303		$ 26			577,277
Exercise of stock options, Shares			25,581
Unrealized gain (loss) on available-for-sale securities	(584,317)							(584,317)
Balance at Sep. 30, 2020	$ 205,119,967		$ 40,096		$ (450,342,422)	$ 654,342,486		$ 1,079,807
Balance, Shares at Sep. 30, 2020			40,096,001