Note 9 - Stock-based Compensation - Stock Option Activity (Details)	9 Months Ended
	Sep. 30, 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)	249,460
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 6.25
Exercised, number of shares (in shares)
Forfeited, number of shares (in shares)	7,050
Forfeited, weighted average exercise price (in dollars per share) | $ / shares	$ 8.45
Options outstanding, number of shares (in shares)	506,810
Options outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 6.89