Note 1 - Summary of Significant Accounting Policies - Option Activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares
Outstanding (in shares) | shares	362,640
Outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 3.96
Granted (in shares) | shares	27,000
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 6.14
Exercised (in shares) | shares	(13,400)
Exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 3.43
Cancelled (in shares) | shares	(10,340)
Cancelled, weighted average exercise price (in dollars per share) | $ / shares	$ 3.42
Outstanding (in shares) | shares	365,900
Outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 4.15
Outstanding, weighted average remaining contractual term (Year)	7 years 3 months
Outstanding, aggregate intrinsic value | $	$ 2,688
Exercisable (in shares) | shares	180,500
Exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 3.75
Exercisable, weighted average remaining contractual term (Year)	6 years 6 months 21 days
Exercisable, aggregate intrinsic value | $	$ 1,398