Note 14 - Stock Option Plans - Summary of Exercise Prices, Weighted Average Remaining Contractual Life and Intrinsic Values of Outstanding Options (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) $ / shares shares
Number outstanding (in shares) | shares	754,497
Weighted average exercise price per share, options outstanding (in dollars per share)	$ 49.94
Weighted average remaining contractual life, options outstanding (Year)	4 years 146 days
Aggregate intrinsic value, options outstanding | $	$ 9,224
Number exercisable (in shares) | shares	356,066
Weighted average exercise price per share, options exercisable (in dollars per share)	$ 40.64
Weighted average remaining contractual life, options exercisable (Year)	3 years 73 days
Aggregate intrinsic value, options exercisable | $	$ 7,590
Exercise Price Range 01 [Member]
Exercise price - lower (in dollars per share)	$ 8.56
Exercise price - higher (in dollars per share)	$ 8.56
Number outstanding (in shares) | shares	19,535
Weighted average exercise price per share, options outstanding (in dollars per share)	$ 8.56
Weighted average remaining contractual life, options outstanding (Year)	146 days
Aggregate intrinsic value, options outstanding | $	$ 1,040
Number exercisable (in shares) | shares	19,535
Weighted average exercise price per share, options exercisable (in dollars per share)	$ 8.56
Weighted average remaining contractual life, options exercisable (Year)	146 days
Aggregate intrinsic value, options exercisable | $	$ 1,039
Exercise Price Range 02 [Member]
Exercise price - lower (in dollars per share)	$ 10.16
Exercise price - higher (in dollars per share)	$ 19.95
Number outstanding (in shares) | shares	74,465
Weighted average exercise price per share, options outstanding (in dollars per share)	$ 16.42
Weighted average remaining contractual life, options outstanding (Year)	1 year 255 days
Aggregate intrinsic value, options outstanding | $	$ 3,378
Number exercisable (in shares) | shares	73,215
Weighted average exercise price per share, options exercisable (in dollars per share)	$ 16.36
Weighted average remaining contractual life, options exercisable (Year)	1 year 255 days
Aggregate intrinsic value, options exercisable | $	$ 3,326
Exercise Price Range 03 [Member]
Exercise price - lower (in dollars per share)	$ 21.10
Exercise price - higher (in dollars per share)	$ 27.53
Number outstanding (in shares) | shares	58,750
Weighted average exercise price per share, options outstanding (in dollars per share)	$ 23.73
Weighted average remaining contractual life, options outstanding (Year)	2 years 36 days
Aggregate intrinsic value, options outstanding | $	$ 2,236
Number exercisable (in shares) | shares	48,750
Weighted average exercise price per share, options exercisable (in dollars per share)	$ 24.27
Weighted average remaining contractual life, options exercisable (Year)	1 year 328 days
Aggregate intrinsic value, options exercisable | $	$ 1,829
Exercise Price Range 04 [Member]
Exercise price - lower (in dollars per share)	$ 35.25
Exercise price - higher (in dollars per share)	$ 37.35
Number outstanding (in shares) | shares	14,375
Weighted average exercise price per share, options outstanding (in dollars per share)	$ 35.89
Weighted average remaining contractual life, options outstanding (Year)	3 years 146 days
Aggregate intrinsic value, options outstanding | $	$ 372
Number exercisable (in shares) | shares	11,875
Weighted average exercise price per share, options exercisable (in dollars per share)	$ 36.02
Weighted average remaining contractual life, options exercisable (Year)	3 years 109 days
Aggregate intrinsic value, options exercisable | $	$ 306
Exercise Price Range 05 [Member]
Exercise price - lower (in dollars per share)	$ 47
Exercise price - higher (in dollars per share)	$ 47
Number outstanding (in shares) | shares	5,000
Weighted average exercise price per share, options outstanding (in dollars per share)	$ 47
Weighted average remaining contractual life, options outstanding (Year)	4 years 73 days
Aggregate intrinsic value, options outstanding | $	$ 74
Number exercisable (in shares) | shares	2,500
Weighted average exercise price per share, options exercisable (in dollars per share)	$ 47
Weighted average remaining contractual life, options exercisable (Year)	4 years 73 days
Aggregate intrinsic value, options exercisable | $	$ 37
Exercise Price Range 06 [Member]
Exercise price - lower (in dollars per share)	$ 53.20
Exercise price - higher (in dollars per share)	$ 58.65
Number outstanding (in shares) | shares	340,078
Weighted average exercise price per share, options outstanding (in dollars per share)	$ 55.53
Weighted average remaining contractual life, options outstanding (Year)	4 years 182 days
Aggregate intrinsic value, options outstanding | $	$ 2,124
Number exercisable (in shares) | shares	172,802
Weighted average exercise price per share, options exercisable (in dollars per share)	$ 55.68
Weighted average remaining contractual life, options exercisable (Year)	4 years 73 days
Aggregate intrinsic value, options exercisable | $	$ 1,053
Exercise Price Range 07 [Member]
Exercise price - lower (in dollars per share)	$ 61.33
Exercise price - higher (in dollars per share)	$ 64.10
Number outstanding (in shares) | shares	242,294
Weighted average exercise price per share, options outstanding (in dollars per share)	$ 62.99
Weighted average remaining contractual life, options outstanding (Year)	6 years
Aggregate intrinsic value, options outstanding | $
Number exercisable (in shares) | shares	27,389
Weighted average exercise price per share, options exercisable (in dollars per share)	$ 64.10
Weighted average remaining contractual life, options exercisable (Year)	5 years 146 days
Aggregate intrinsic value, options exercisable | $