Note 13 - Stock-based Compensation - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Options outstanding (in shares)	229,531	276,266	252,616
Options outstanding, weighted-average exercise price (in dollars per share)	$ 86.46	$ 72.38	$ 64.71
Granted (in shares)	57,901	60,065	53,708
Granted, weighted-average exercise price (in dollars per share)	$ 128.14	$ 105.79	$ 105.81
Exercised (in shares)	(28,991)	(68,958)	(16,079)
Exercised, weighted-average exercise price (in dollars per share)	$ 58.78	$ 57.00	$ 48.67
Cancelled (in shares)	(25,057)	(37,842)	(13,979)
Cancelled, weighted-average exercise price (in dollars per share)	$ 109.31	$ 67.92	$ 89.50
Options outstanding (in shares)	233,384	229,531	276,266
Options outstanding, weighted-average exercise price (in dollars per share)	$ 97.78	$ 86.46	$ 72.38
Options exercisable (in shares)	115,700
Options exercisable, weighted-average exercise price (in dollars per share)	$ 81.30