Note 1 - Summary of Significant Accounting Policies - Option Activity (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 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
Granted, weighted average exercise price (in dollars per share) | $ / shares
Exercised (in shares) | shares	(1,000)
Exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 3.70
Cancelled (in shares) | shares	(6,140)
Cancelled, weighted average exercise price (in dollars per share) | $ / shares	$ 3.40
Outstanding (in shares) | shares	355,500
Outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 3.97
Outstanding, weighted average remaining contractual term (Year)	7 years 189 days
Outstanding, aggregate intrinsic value | $	$ 821
Exercisable (in shares) | shares	173,700
Exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 3.77
Exercisable, weighted average remaining contractual term (Year)	6 years 361 days
Exercisable, aggregate intrinsic value | $	$ 437