Note 2 - Summary of Significant Accounting Policies - Antidilutive Securities Excluded From Computation of Earnings Per Share (Details) - shares		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Total potential dilutive securities (in shares)	[1]	5,818,431	4,912,152
Share-based Payment Arrangement, Option [Member]
Total potential dilutive securities (in shares)	[1]	1,040,522	1,709,106
Restricted Stock Units (RSUs) [Member]
Total potential dilutive securities (in shares)		4,771,537	2,397,299
Warrant [Member]
Total potential dilutive securities (in shares)	[1]	6,372	805,747

[1] The number of shares is based on the maximum number of shares issuable on exercise or conversion of the related securities as of the period end. Such amounts have not been adjusted for the treasury stock method or weighted average outstanding calculations as required if the securities were dilutive.