Note 10 - Basic and Diluted Net Loss per Share - Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	9,994,096	53,699,803
Share-based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	5,089,464	4,285,880
Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	1,013,383	46,498,909
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	3,891,249	2,915,014