Note 5 - Stock Based Compensation - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Outstanding, shares (in shares)	188,033	23,333
Weighted-average exercise price per share, outstanding (in dollars per share)	$ 7.19	$ 7.38	$ 9.49
Weighted-average remaining contractual term, outstanding (Year)	8 years 229 days	8 years 229 days	6 years 156 days
Granted, shares (in shares)	0	165,300
Weighted-average exercise price per share, granted (in dollars per share)		$ 7.08
Exercised, shares (in shares)	(5,500)	(600)
Weighted-average exercise price per share, exercised (in dollars per share)	$ 7.08	$ 7.08
Forfeited, canceled or expired, shares (in shares)	(4,533)
Weighted-average exercise price per share, forfeited or expired (in dollars per share)	$ 15.23
Outstanding, shares (in shares)	178,000	188,033	23,333
Exercisable, shares (in shares)	178,000
Weighted-average exercise price per share, exercisable (in dollars per share)	$ 7.19
Weighted-average remaining contractual term, exercisable (Year)	8 years 229 days