Note 15 - Stock-based Compensation - Options Outstanding (Details)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Number outstanding (in shares) | shares	469,572
Number exercisable (in shares) | shares	358,270
$7.99 to $8.93
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	24,175
Weighted average remaining contractual life (Year)	2 years 26 days
Weighted average exercise price options outstanding (in dollars per share)	$ 8.10
Number exercisable (in shares) | shares	24,175
Weighted average exercise price options exercisable (in dollars per share)	$ 8.10
$9.00 to $9.30
Exercise price range, lower range (in dollars per share)	9.00
Exercise price range, upper range (in dollars per share)	$ 9.30
Number outstanding (in shares) | shares	121,724
Weighted average remaining contractual life (Year)	2 years 1 month 6 days
Weighted average exercise price options outstanding (in dollars per share)	$ 9.21
Number exercisable (in shares) | shares	121,724
Weighted average exercise price options exercisable (in dollars per share)	$ 9.21
$15.08 to $16.13
Exercise price range, lower range (in dollars per share)	15.08
Exercise price range, upper range (in dollars per share)	$ 16.13
Number outstanding (in shares) | shares	74,703
Weighted average remaining contractual life (Year)	4 years 2 months 27 days
Weighted average exercise price options outstanding (in dollars per share)	$ 15.63
Number exercisable (in shares) | shares	72,303
Weighted average exercise price options exercisable (in dollars per share)	$ 15.64
$17.10 to $18.00
Exercise price range, lower range (in dollars per share)	17.10
Exercise price range, upper range (in dollars per share)	$ 18.00
Number outstanding (in shares) | shares	125,137
Weighted average remaining contractual life (Year)	5 years 6 months 22 days
Weighted average exercise price options outstanding (in dollars per share)	$ 17.31
Number exercisable (in shares) | shares	99,573
Weighted average exercise price options exercisable (in dollars per share)	$ 17.29
$21.71 to $31.53
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	66,291
Weighted average remaining contractual life (Year)	7 years 1 month 10 days
Weighted average exercise price options outstanding (in dollars per share)	$ 22.92
Number exercisable (in shares) | shares	29,633
Weighted average exercise price options exercisable (in dollars per share)	$ 22.64
$42.65 to $48.50
Exercise price range, lower range (in dollars per share)	42.65
Exercise price range, upper range (in dollars per share)	$ 48.50
Number outstanding (in shares) | shares	57,542
Weighted average remaining contractual life (Year)	8 years 5 months 16 days
Weighted average exercise price options outstanding (in dollars per share)	$ 43.94
Number exercisable (in shares) | shares	10,862
Weighted average exercise price options exercisable (in dollars per share)	$ 43.79