Note 13 - Stock-based Compensation Plan - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Options outstanding, number of shares (in shares)	19,800
Options outstanding, weighted average exercise price (in dollars per share)
Granted, number of shares (in shares)	96,000	19,800
Granted, weighted average exercise price (in dollars per share)	$ 6.35	$ 4.37
Canceled, number of shares (in shares)	39,400
Canceled, weighted average exercise price (in dollars per share)	$ 6.08
Canceled, number of shares (in shares)	(39,400)
Options outstanding, weighted average exercise price (in dollars per share)	$ 5.98
Options outstanding, number of shares (in shares)	76,400	19,800