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Note 13 - Share-based Payments - Summary of Exercise Prices, Weighted Average Remaining Contractual Life and Intrinsic Values of Outstanding Options (Details)
 9 Months Ended
Sep. 30, 2017
USD ($)
$ / shares
shares
Number outstanding (in shares) | shares 659,657
Weighted average exercise price per share, options outstanding (in dollars per share) $ 36.39
Weighted average remaining contractual life, options outstanding (Year) 5 years 36 days
Aggregate intrinsic value, options outstanding | $ $ 14,620,730
Number exercisable (in shares) | shares 223,043
Weighted average exercise price per share, options exercisable (in dollars per share) $ 14.30
Weighted average remaining contractual life, options exercisable (Year) 2 years 328 days
Aggregate intrinsic value, options exercisable | $ $ 9,868,866
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 96,644
Weighted average exercise price per share, options outstanding (in dollars per share) $ 6.72
Weighted average remaining contractual life, options outstanding (Year) 1 year 328 days
Aggregate intrinsic value, options outstanding | $ $ 5,008,805
Number exercisable (in shares) | shares 96,644
Weighted average exercise price per share, options exercisable (in dollars per share) $ 6.72
Weighted average remaining contractual life, options exercisable (Year) 1 year 328 days
Aggregate intrinsic value, options exercisable | $ $ 5,008,805
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 122,938
Weighted average exercise price per share, options outstanding (in dollars per share) $ 16.29
Weighted average remaining contractual life, options outstanding (Year) 3 years 255 days
Aggregate intrinsic value, options outstanding | $ $ 5,195,152
Number exercisable (in shares) | shares 76,399
Weighted average exercise price per share, options exercisable (in dollars per share) $ 15.99
Weighted average remaining contractual life, options exercisable (Year) 3 years 182 days
Aggregate intrinsic value, options exercisable | $ $ 3,251,248
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 81,000
Weighted average exercise price per share, options outstanding (in dollars per share) $ 23.65
Weighted average remaining contractual life, options outstanding (Year) 4 years 146 days
Aggregate intrinsic value, options outstanding | $ $ 2,826,893
Number exercisable (in shares) | shares 45,000
Weighted average exercise price per share, options exercisable (in dollars per share) $ 25.39
Weighted average remaining contractual life, options exercisable (Year) 3 years 255 days
Aggregate intrinsic value, options exercisable | $ $ 1,492,313
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) 5 years 255 days
Aggregate intrinsic value, options outstanding | $ $ 325,750
Number exercisable (in shares) | shares 5,000
Weighted average exercise price per share, options exercisable (in dollars per share) $ 35.25
Weighted average remaining contractual life, options exercisable (Year) 6 years 73 days
Aggregate intrinsic value, options exercisable | $ $ 116,500
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) 6 years 109 days
Aggregate intrinsic value, options outstanding | $ $ 265,650
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 | $
Exercise Price Range 06 [Member]  
Exercise price - lower (in dollars per share)
Exercise price - higher (in dollars per share) $ 55.65
Number outstanding (in shares) | shares 326,200
Weighted average exercise price per share, options outstanding (in dollars per share) $ 55.49
Weighted average remaining contractual life, options outstanding (Year) 6 years 255 days
Aggregate intrinsic value, options outstanding | $ $ 998,480
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 | $