Note 9 - Stock-based Compensation - Unvested Stock Activity (Details)	6 Months Ended
	Jun. 30, 2019 $ / shares shares
Granted, number of shares (in shares)	239,160
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)	115,680
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 6.57
Vested, number of shares (in shares)	(43,724)
Vested, weighted average exercise price (in dollars per share) | $ / shares	$ 6.90
Forfeited, number of shares (in shares)	(12,325)
Forfeited, weighted average exercise price (in dollars per share) | $ / shares	$ 7.14
Unvested shares (in shares)	174,381
Unvested shares, weighted average exercise price (in dollars per share) | $ / shares	$ 6.68