Note 9 - Stock-based Compensation - Stock Option Activity (Details)	3 Months Ended
	Mar. 31, 2019 $ / shares shares
Options outstanding, number of shares (in shares)	264,400
Options outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 7.54
Granted, number of shares (in shares)	132,600
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 7.13
Exercised, number of shares (in shares)
Forfeited, number of shares (in shares)
Options outstanding, number of shares (in shares)	397,000
Options outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 7.40