CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ (32,943,583)	$ (39,911,175)	$ (32,012,304)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	133,879	99,572	94,211
Stock-based compensation	5,561,895	6,625,743	5,646,852
Changes in operating assets and liabilities:
Incentive and tax receivables	(11,169,349)	538,984	(369,661)
Prepaid expenses and other assets	1,561,780	(1,291,186)	(324,304)
Deferred grant revenue		(833,975)
Right-of-use assets	(5,307)
Accounts payable	209,613	1,103,013	1,492,171
Accrued expenses	1,833,096	1,271,673	(369,416)
Net cash used in operating activities	(34,817,976)	(32,397,351)	(25,842,451)
Cash flows from investing activities:
Purchases of property and equipment	(129,390)	(286,658)	(115,356)
Net cash used in investing activities	(129,390)	(286,658)	(115,356)
Cash flows from financing activities:
Proceeds from the issuance of common stock, net of issuance costs	45,187,070	29,937,505	57,293,041
Payment of deferred financing costs	(129,935)		(225,439)
Proceeds from the exercise of stock options	189,700		434,691
Net cash provided by financing activities	45,246,835	29,937,505	57,502,293
Net increase (decrease) in cash and cash equivalents	10,299,469	(2,746,504)	31,544,486
Cash and cash equivalents at beginning of year	59,763,773	62,510,277	30,965,791
Cash and cash equivalents at end of year	70,063,242	59,763,773	62,510,277
Supplemental disclosures of cash flow information:
Deferred financing costs included in accounts payable and accrued expenses	63,570	60,000	$ 15,000
Changes in property and equipment acquired but not paid	4,750	$ 20,350
Reclassification of deferred rent liability to right-of-use assets upon adoption of ASC 842	12,824
Right-of-use assets and lease liability recorded upon adoption of ASC 842	$ 325,683