Note 9 - Stock-based Compensation - Stock Option Activity (Details)	9 Months Ended
	Sep. 30, 2017 $ / shares shares
Options outstanding, Number of shares (in shares) | shares	19,800
Options outstanding, Weighted average grant date fair value (in dollars per share) | $ / shares	$ 4.37
Granted, Number of shares (in shares) | shares	96,000
Granted, Weighted average grant date fair value (in dollars per share) | $ / shares	$ 6.35
Options outstanding, Number of shares (in shares) | shares	115,800
Options outstanding, Weighted average grant date fair value (in dollars per share) | $ / shares	$ 6.01