Note 7 - Stock Plans - Non-vested Restricted Stock (Details) - Restricted Stock [Member] - $ / shares	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Non-vested balance (in shares)	43,043
Outstanding, weighted average grant date fair value (in dollars per share)	$ 53.20
Granted (in shares)	34,570
Granted, weighted average grant date fair value (in dollars per share)	$ 49.83	$ 52.02
Forfeited (in shares)	(1,533)
Forfeited, weighted average grant date fair value (in dollars per share)	$ 52.26
Vested (in shares)	(11,541)
Vested, weighted average grant date fair value (in dollars per share)	$ 52.84
Non-vested balance (in shares)	64,539
Outstanding, weighted average grant date fair value (in dollars per share)	$ 51.48
The 2012 Director Stock Incentive Plan [Member]
Non-vested balance (in shares)	14,920
Granted (in shares)	18,000
Granted, weighted average grant date fair value (in dollars per share)	$ 49.85	$ 52.00
Forfeited (in shares)	0
Vested (in shares)	(9,048)
Non-vested balance (in shares)	23,872
The 2012 Omnibus Stock Incentive Plan [Member]
Non-vested balance (in shares)	28,123
Granted (in shares)	16,570
Forfeited (in shares)	(1,533)
Vested (in shares)	(2,493)
Non-vested balance (in shares)	40,667