Note 6 - Share-based Compensation - Stock Option Transactions (Details) $ / shares in Units, $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares		Dec. 31, 2018 USD ($) $ / shares shares
Outstanding, January 1, 2019 (in shares) | shares	676,846
Outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 15.70
Outstanding, weighted average remaining life (Year)	3 years 73 days		2 years 361 days
Outstanding, aggregate intrinsic value | $	$ 984		$ 2,230
Granted (in shares) | shares	184,994	[1]
Granted, weighted average exercise price (in dollars per share) | $ / shares	$ 17.22	[1]
Exercised (in shares) | shares	(75,444)
Exercised, weighted average exercise price (in dollars per share) | $ / shares	$ 6.71
Cancelled (in shares) | shares	(80,005)
Cancelled, weighted average exercise price (in dollars per share) | $ / shares	$ 17.71
Outstanding, September 30, 2019 (in shares) | shares	706,391		676,846
Outstanding, weighted average exercise price (in dollars per share) | $ / shares	$ 16.83		$ 15.70
Options exercisable, September 30, 2019 (in shares) | shares	497,993
Options exercisable, weighted average exercise price (in dollars per share) | $ / shares	$ 16.56
Options exercisable, weighted average remaining life (Year)	2 years 211 days
Options exercisable, aggregate intrinsic value | $	$ 967

[1] The weighted average grant date fair value of stock options granted was $3.96 per share.