Note 10 - Stock-based Compensation - Summary of Restricted Stock Activity (Details) - Restricted Stock [Member] - Mercantile Plans [Member]	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Nonvested at beginning of year (in shares) | shares	374,771
Nonvested at beginning of year (in dollars per share) | $ / shares	$ 30.49
Granted (in shares) | shares	95,084
Granted (in dollars per share) | $ / shares	$ 40.23
Vested (in shares) | shares	(109,414)
Vested (in dollars per share) | $ / shares	$ 27.01
Forfeited (in shares) | shares	(4,551)
Forfeited (in dollars per share) | $ / shares	$ 28.7
Nonvested at end of year (in shares) | shares	355,890
Nonvested at end of year (in dollars per share) | $ / shares	$ 34.18