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Note 14 - Share-based Payments - Summary of Exercise Prices, Weighted Average Remaining Contractual Life and Intrinsic Values of Outstanding Options (Details)
 3 Months Ended
Mar. 31, 2018
USD ($)
$ / shares
shares
Number outstanding (in shares) | shares 634,883
Weighted average exercise price per share, options outstanding (in dollars per share) $ 37.48
Weighted average remaining contractual life, options outstanding (Year) 4 years
Aggregate intrinsic value, options outstanding | $ $ 11,782,970
Number exercisable (in shares) | shares 245,933
Weighted average exercise price per share, options exercisable (in dollars per share) $ 16.62
Weighted average remaining contractual life, options exercisable (Year) 2 years
Aggregate intrinsic value, options exercisable | $ $ 9,685,617
Exercise Price Range 01 [Member]  
Exercise price - lower (in dollars per share) $ 2.92
Exercise price - higher (in dollars per share) $ 8.92
Number outstanding (in shares) | shares 81,695
Weighted average exercise price per share, options outstanding (in dollars per share) $ 6.81
Weighted average remaining contractual life, options outstanding (Year) 255 days
Aggregate intrinsic value, options outstanding | $ $ 4,018,538
Number exercisable (in shares) | shares 81,695
Weighted average exercise price per share, options exercisable (in dollars per share) $ 6.81
Weighted average remaining contractual life, options exercisable (Year) 255 days
Aggregate intrinsic value, options exercisable | $ $ 4,018,538
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 117,013
Weighted average exercise price per share, options outstanding (in dollars per share) $ 16.31
Weighted average remaining contractual life, options outstanding (Year) 2 years 182 days
Aggregate intrinsic value, options outstanding | $ $ 4,644,246
Number exercisable (in shares) | shares 90,613
Weighted average exercise price per share, options exercisable (in dollars per share) $ 15.93
Weighted average remaining contractual life, options exercisable (Year) 2 years 109 days
Aggregate intrinsic value, options exercisable | $ $ 3,631,248
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 75,000
Weighted average exercise price per share, options outstanding (in dollars per share) $ 23.67
Weighted average remaining contractual life, options outstanding (Year) 3 years 36 days
Aggregate intrinsic value, options outstanding | $ $ 2,424,562
Number exercisable (in shares) | shares 55,000
Weighted average exercise price per share, options exercisable (in dollars per share) $ 24.61
Weighted average remaining contractual life, options exercisable (Year) 2 years 292 days
Aggregate intrinsic value, options exercisable | $ $ 1,726,562
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) 4 years 146 days
Aggregate intrinsic value, options outstanding | $ $ 289,094
Number exercisable (in shares) | shares 10,625
Weighted average exercise price per share, options exercisable (in dollars per share) $ 36.11
Weighted average remaining contractual life, options exercisable (Year) 4 years 73 days
Aggregate intrinsic value, options exercisable | $ $ 211,281
Exercise Price Range 05 [Member]  
Exercise price - lower (in dollars per share) $ 43.15
Exercise price - higher (in dollars per share) $ 47
Number outstanding (in shares) | shares 18,500
Weighted average exercise price per share, options outstanding (in dollars per share) $ 44.19
Weighted average remaining contractual life, options outstanding (Year) 5 years 36 days
Aggregate intrinsic value, options outstanding | $ $ 218,475
Number exercisable (in shares) | shares 8,000
Weighted average exercise price per share, options exercisable (in dollars per share) $ 43.75
Weighted average remaining contractual life, options exercisable (Year) 5 years 36 days
Aggregate intrinsic value, options exercisable | $ $ 97,988
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 328,300
Weighted average exercise price per share, options outstanding (in dollars per share) $ 55.51
Weighted average remaining contractual life, options outstanding (Year) 5 years 146 days
Aggregate intrinsic value, options outstanding | $ $ 188,055
Number exercisable (in shares) | shares
Weighted average exercise price per share, options exercisable (in dollars per share)
Weighted average remaining contractual life, options exercisable (Year)
Aggregate intrinsic value, options exercisable | $