Note 1 - Summary of Significant Accounting Policies - Stock Option Activity (Details)	3 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares	Sep. 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	16,700	186,200
Granted, weighted average exercise price per share (in dollars per share) | $ / shares		$ 4.31
Exercised (in shares) | shares		(2,250)
Exercised, weighted average exercise price per share (in dollars per share) | $ / shares		$ 3.20
Cancelled (in shares) | shares		(109,700)
Cancelled, weighted average exercise price per share (in dollars per share) | $ / shares		$ 3.50
Outstanding (in shares) | shares	299,000	299,000
Outstanding, weighted average exercise price per share (in dollars per share) | $ / shares	$ 3.96	$ 3.96
Outstanding, weighted average remaining contractual term (Year)		9 years 47 days
Outstanding, aggregate intrinsic value | $
Exercisable (in shares) | shares	26,867	26,867
Exercisable, weighted average exercise price per share (in dollars per share) | $ / shares	$ 3.41	$ 3.41
Exercisable, weighted average remaining contractual term (Year)		8 years 167 days
Exercisable, aggregate intrinsic value | $