Net loss per share, Anti-dilutive Securities Excluded from Computation of Net Loss per Share (Details) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Series A Warrants and Series B Warrants [Member]
Net Loss Per Share [Abstract]
Antidilutive securities excluded from computation of net loss per share (in shares)	7,374,172	0
Stock Options [Member]
Net Loss Per Share [Abstract]
Antidilutive securities excluded from computation of net loss per share (in shares)	1,818,612	1,029,781
Restricted Stock Awards [Member]
Net Loss Per Share [Abstract]
Antidilutive securities excluded from computation of net loss per share (in shares)	4,474	0
Former Rexahn Warrants [Member]
Net Loss Per Share [Abstract]
Antidilutive securities excluded from computation of net loss per share (in shares)	66,538	0
Former Rexahn Options [Member]
Net Loss Per Share [Abstract]
Antidilutive securities excluded from computation of net loss per share (in shares)	123	0