Note 11 - Stock-based Compensation - Summary of Information Related to Options Outstanding (Details) - Mercantile Plans [Member] - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Minimum exercise price (in dollars per share)	$ 27.66	$ 22.15	$ 5.19
Maximum exercise price (in dollars per share)	$ 36.22	$ 36.22	$ 36.22
Average remaining option term (Year)	1 year 8 months 12 days	2 years 4 months 24 days	3 years 2 months 12 days