Note 15 - Stock-based Compensation - Summary of Options Outstanding (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Options outstanding, shares (in shares)	866,956	809,529
Options outstanding, weighted average exercise price (in dollars per share)	$ 72.11	$ 71.24
Options granted, shares (in shares)	56,795	104,057
Options granted, weighted average exercise price (in dollars per share)	$ 70.73	$ 73.98
Options exercised, shares (in shares)	(148,900)	(43,630)
Options exercised, weighted average exercise price (in dollars per share)	$ 68.41	$ 63.37
Options cancelled, shares (in shares)	(6,000)	(3,000)
Options cancelled, weighted average exercise price (in dollars per share)	$ 72.94	$ 72.94
Options outstanding, shares (in shares)	768,851	866,956
Options outstanding, weighted average exercise price (in dollars per share)	$ 72.72	$ 72.11
Options outstanding, aggregate intrinsic value	$ 656,425
Options exercisable, shares (in shares)	177,686
Options exercisable, weighted average exercise price (in dollars per share)	$ 69.38
Options exercisable, aggregate intrinsic value	$ 587,578