Note 1 - Summary of Significant Accounting Policies - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) $ / shares shares
Outstanding (in shares) | shares	372,200
Outstanding, weighted average exercise price per share (in dollars per share) | $ / shares	$ 3.85
Granted (in shares) | shares	11,300
Granted, weighted average exercise price per share (in dollars per share) | $ / shares	$ 2.95
Cancelled (in shares) | shares	(3,200)
Cancelled, weighted average exercise price per share (in dollars per share) | $ / shares	$ 3.29
Outstanding (in shares) | shares	380,300
Outstanding, weighted average exercise price per share (in dollars per share) | $ / shares	$ 3.83
Outstanding, weighted average remaining contractual term (Year)	8 years 135 days
Outstanding, aggregate intrinsic value | $	$ 24,285
Exercisable (in shares) | shares	107,557
Exercisable, weighted average exercise price per share (in dollars per share) | $ / shares	$ 4.06
Exercisable, weighted average remaining contractual term (Year)	7 years 160 days
Exercisable, aggregate intrinsic value | $	$ 8,095