Note 8 - Stockholders' Equity - Summary of Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Options outstanding, beginning of year (in shares)	140,424	236,844
Options outstanding, beginning of year, weighted average exercise price (in dollars per share)	$ 7.85	$ 8.14
Options granted (in shares)
Options granted, weighted average exercise price (in dollars per share)
Options exercised (in shares)
Options exercised, weighted average exercise price (in dollars per share)
Options expired and forfeited (in shares)	(58,998)	(96,420)
Options expired and forfeited, weighted average exercise price (in dollars per share)	$ 7.96	$ 8.57
Options outstanding, end of year (in shares)	81,426	140,424
Options outstanding, end of year, weighted average exercise price (in dollars per share)	$ 7.77	$ 7.85
Options exercisable (in shares)	14,655	13,713
Options exercisable, weighted average exercise price (in dollars per share)	$ 7.77	$ 7.77