Note 15 - Stock-based Compensation - Options Outstanding (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Number outstanding (in shares) | shares	513,554
Number exercisable (in shares) | shares	354,269
Range 1 [Member]
Exercise price range, lower range (in dollars per share)	$ 7.99
Exercise price range, upper range (in dollars per share)	$ 8.93
Number outstanding (in shares) | shares	27,850
Weighted average remaining contractual life (Year)	3 years 21 days
Weighted average exercise price options outstanding (in dollars per share)	$ 8.09
Number exercisable (in shares) | shares	27,850
Weighted average exercise price options exercisable (in dollars per share)	$ 8.09
Range 2 [Member]
Exercise price range, lower range (in dollars per share)	9
Exercise price range, upper range (in dollars per share)	$ 9.30
Number outstanding (in shares) | shares	148,755
Weighted average remaining contractual life (Year)	2 years 281 days
Weighted average exercise price options outstanding (in dollars per share)	$ 9.22
Number exercisable (in shares) | shares	147,955
Weighted average exercise price options exercisable (in dollars per share)	$ 9.22
Range 3 [Member]
Exercise price range, lower range (in dollars per share)	15
Exercise price range, upper range (in dollars per share)	$ 16.85
Number outstanding (in shares) | shares	90,668
Weighted average remaining contractual life (Year)	4 years 215 days
Weighted average exercise price options outstanding (in dollars per share)	$ 15.63
Number exercisable (in shares) | shares	79,369
Weighted average exercise price options exercisable (in dollars per share)	$ 15.64
Range 4 [Member]
Exercise price range, lower range (in dollars per share)	17.10
Exercise price range, upper range (in dollars per share)	$ 18
Number outstanding (in shares) | shares	132,816
Weighted average remaining contractual life (Year)	6 years 208 days
Weighted average exercise price options outstanding (in dollars per share)	$ 17.31
Number exercisable (in shares) | shares	81,521
Weighted average exercise price options exercisable (in dollars per share)	$ 17.26
Range 5 [Member]
Exercise price range, lower range (in dollars per share)	21.71
Exercise price range, upper range (in dollars per share)	$ 31.53
Number outstanding (in shares) | shares	70,215
Weighted average remaining contractual life (Year)	8 years 29 days
Weighted average exercise price options outstanding (in dollars per share)	$ 22.63
Number exercisable (in shares) | shares	16,273
Weighted average exercise price options exercisable (in dollars per share)	$ 22.64
Range 6 [Member]
Exercise price range, upper range (in dollars per share)	$ 48.50
Number outstanding (in shares) | shares	43,250
Weighted average remaining contractual life (Year)	9 years 73 days
Weighted average exercise price options outstanding (in dollars per share)	$ 43.86
Number exercisable (in shares) | shares	1,301
Weighted average exercise price options exercisable (in dollars per share)	$ 42.75