Note 10 - Stock-based Compensation - Stock Option Activity (Details)	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Options outstanding, number of shares (in shares)	76,400
Options outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 5.98
Granted, number of shares (in shares)	140,700
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 8.45
Exercised, number of shares (in shares)
Options outstanding, number of shares (in shares)	217,100
Options outstanding, number of shares (in dollars per share) | $ / shares	$ 7.58
Restricted Stock [Member]
Forfeited, number of shares (in shares)