Note 10 - Stock-based Compensation Plan - Unvested Stock Activity (Details) - Restricted Stock [Member]	9 Months Ended
	Sep. 30, 2020 $ / shares shares
Unvested shares outstanding (in shares) | shares	165,031
Granted, number of shares (in shares) | shares	229,110
Vested, number of shares (in shares) | shares	(80,361)
Forfeited, number of shares (in shares) | shares	(67,125)
Unvested shares outstanding (in shares) | shares	246,655
Unvested shares outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 6.55
Granted, weighted average exercise price (in dollars per share) | $ / shares	4.24
Vested, weighted average exercise price (in dollars per share) | $ / shares	5.47
Forfeited, weighted average exercise price (in dollars per share) | $ / shares	6.03
Unvested shares outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 4.89