Note 2 - Summary of Significant Accounting Policies - Antidilutive Securities (Details) - shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Share-based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	50,471	42,917
Common Stock Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	5,549	6,408
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)	3,432	600