Note 9 - Stock-based Compensation - Unvested Stock Activity (Details)	3 Months Ended
	Mar. 31, 2019 $ / shares shares
Granted, number of shares (in shares)	132,600
Restricted Stock [Member]
Unvested shares (in shares)	114,750
Unvested shares, weighted average exercise price (in dollars per share) | $ / shares	$ 6.92
Granted, number of shares (in shares)	80,300
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 7.13
Vested, number of shares (in shares)	(34,000)
Vested, weighted average exercise price (in dollars per share) | $ / shares	$ 6.82
Forfeited, number of shares (in shares)
Forfeited, weighted average exercise price (in dollars per share) | $ / shares
Unvested shares (in shares)	161,050
Unvested shares, weighted average exercise price (in dollars per share) | $ / shares	$ 7.04