Note 5 - Stock-based Compensation (Details) - Stock Option Activity $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($) $ / shares shares
Stock Option Activity [Abstract]
Outstanding at January 1, 2015 | shares	278,925
Outstanding at January 1, 2015	$ 15.74
Granted | shares	500
Granted	$ 25.59
Exercised | shares	(35,045)
Exercised	$ 14.96
Outstanding at September 30, 2015 | shares	244,380
Outstanding at September 30, 2015	$ 15.87
Outstanding at September 30, 2015	3 years 131 days
Outstanding at September 30, 2015 | $	$ 2,726
Exercisable at September 30, 2015 | shares	230,381
Exercisable at September 30, 2015	$ 15.65
Exercisable at September 30, 2015	3 years 87 days
Exercisable at September 30, 2015 | $	$ 2,622