Note 10 - Net Loss Per Share - Schedule of Antidilutive Securities (Details) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Number of potential common shares excluded (in shares)	32,321,523	5,569,028
Share-based Payment Arrangement, Option [Member]
Number of potential common shares excluded (in shares)	7,067,436	4,308,383
Series B Convertible Preferred Stock [Member]
Number of potential common shares excluded (in shares)	177,373	190,617
Warrant [Member]
Number of potential common shares excluded (in shares)	25,076,714	1,070,028