Note 12 - Net Loss Per Share - Anti-dilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive securities (in shares)	3,294,253	934,541	479,010
Share-based Payment Arrangement, Option [Member]
Antidilutive securities (in shares)	821,464	608,547	468,122
Restricted Stock Units (RSUs) [Member]
Antidilutive securities (in shares)	36,981	29,698	10,888
Warrant [Member]
Antidilutive securities (in shares)	2,435,808	296,296