Note 15 - Share-based Payments - Stock Option Transactions (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Outstanding, Number of shares (in shares)	991,097	897,278	845,020	754,497
Outstanding, Weighted average exercise price per share (in dollars per share)	$ 61.81	$ 53.41	$ 55.31	$ 49.94
Granted, Number of shares (in shares)	26,675	23,800	265,725	219,325
Granted, Weighted average exercise price per share (in dollars per share)	$ 76.93	$ 68.30	$ 79.18	$ 60.18
Exercised, Number of shares (in shares)	(46,803)	(38,102)	(120,828)	(80,037)
Exercised, Weighted average exercise price per share (in dollars per share)	$ 46.47	$ 38.58	$ 45.36	$ 26.87
Forfeited, Number of shares (in shares)	(14,087)	(10,678)	(31,649)	(18,993)
Forfeited, Weighted average exercise price per share (in dollars per share)	$ 68.95	$ 60.54	$ 64.54	$ 60.41
Expired, Number of shares (in shares)	(648)	(636)	(2,034)	(3,130)
Expired, Weighted average exercise price per share (in dollars per share)	$ 56.40	$ 58.77	$ 60.17	$ 59.64
Outstanding, Number of shares (in shares)	956,234	871,662	956,234	871,662
Outstanding, Weighted average exercise price per share (in dollars per share)	$ 62.88	$ 54.38	$ 62.88	$ 54.38
Options exercisable, Number of shares (in shares)	470,317	436,862	470,317	436,862
Options exercisable, Weighted average exercise price per share (in dollars per share)	$ 54.87	$ 48.57	$ 54.87	$ 48.57