Note 1 - Summary of Significant Accounting Policies - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2019 USD ($) $ / shares shares
Outstanding (in shares) | shares		224,750
Outstanding, weighted average exercise price per share (in dollars per share) | $ / shares		$ 3.44
Granted (in shares) | shares	137,500	169,500
Granted, weighted average exercise price per share (in dollars per share) | $ / shares		$ 4.44
Exercised (in shares) | shares		(2,250)
Exercised, weighted average exercise price per share (in dollars per share) | $ / shares		$ 3.20
Cancelled (in shares) | shares		(23,250)
Cancelled, weighted average exercise price per share (in dollars per share) | $ / shares		$ 3.85
Outstanding (in shares) | shares	368,750	368,750
Outstanding, weighted average exercise price per share (in dollars per share) | $ / shares	$ 3.88	$ 3.88
Outstanding, weighted average remaining contractual term (Year)		9 years 3 days
Outstanding, aggregate intrinsic value | $	$ 134	$ 134
Exercisable (in shares) | shares	111,817	111,817
Exercisable, weighted average exercise price per share (in dollars per share) | $ / shares	$ 3.46	$ 3.46
Exercisable, weighted average remaining contractual term (Year)		7 years 21 days
Exercisable, aggregate intrinsic value | $	$ 64	$ 64