Note 2 - Basis of Presentation and Summary of Significant Accounting Policies - Common Stock Equivalent Shares Excluded From Calculation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Anti-dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share (in shares)	2,090,783	1,829,037
Share-based Payment Arrangement, Option [Member]
Anti-dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share (in shares)	1,979,411	1,658,112
Warrant [Member]
Anti-dilutive Shares Excluded from Calculation of Diluted Net Loss Per Share (in shares)	111,372	170,925