Note 5 - Stock Based Compensation - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Outstanding, shares (in shares)	178,000	188,033
Weighted-average exercise price per share, outstanding (in dollars per share)	$ 7.19	$ 7.38
Weighted-average remaining contractual term, outstanding (Year)	7 years 178 days	8 years 229 days	8 years 229 days
Granted, shares (in shares)	0	0
Weighted-average exercise price per share, granted (in dollars per share)
Exercised, shares (in shares)		(5,500)
Weighted-average exercise price per share, exercised (in dollars per share)		$ 7.08
Forfeited, canceled or expired, shares (in shares)	(16,667)	(4,533)
Weighted-average exercise price per share, forfeited, canceled or expired (in dollars per share)	$ 7.38	$ 15.23
Outstanding, shares (in shares)	161,333	178,000	188,033
Weighted-average exercise price per share, outstanding (in dollars per share)	$ 7.17	$ 7.19	$ 7.38
Exercisable, shares (in shares)	161,333
Weighted-average exercise price per share, exercisable (in dollars per share)	$ 7.17
Weighted-average remaining contractual term, exercisable (Year)	7 years 178 days