Note 9 - Shareholders' Equity - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares
Options outstanding (in shares) | shares	1,860,211
Options outstanding - weighted average exercise price (in dollars per share) | $ / shares	$ 6.10
Granted (in shares) | shares	217,500
Granted - weighted average exercise price (in dollars per share) | $ / shares	$ 9.68
Exercised (in shares) | shares	(305,460)
Exercised - weighted average exercise price (in dollars per share) | $ / shares	$ 4.54
Forfeited or Expired (in shares) | shares	(17,499)
Forfeited or expired - weighted average exercise price (in dollars per share) | $ / shares	$ 5.61
Options outstanding (in shares) | shares	1,754,752
Options outstanding - weighted average exercise price (in dollars per share) | $ / shares	$ 6.68
Options outstanding - weighted average remaining contractual term (Year)	3 years 182 days
Options outstanding - aggregate intrinsic value | $	$ 3,986
Vested and Expected to Vest (in shares) | shares	1,650,364
Options vested and expected to vest - weighted average exercise price (in dollars per share) | $ / shares	$ 6.66
Options vested and expected to vest - weighted average remaining contractual term (Year)	3 years 131 days
Options vested and expected to vest - aggregate intrinsic value | $	$ 3,791
Options exercisable (in shares) | shares	1,174,378
Exercisable - weighted average exercise price (in dollars per share) | $ / shares	$ 5.75
Exercisable - weighted average remaining contractual term (Year)	2 years 248 days
Exercisable - aggregate intrinsic value | $	$ 3,193