Note 10 - Stock Plans - Non-vested Restricted Stock (Details) - Restricted Stock [Member] - $ / shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Non-vested balance (in shares)	43,043	30,077	27,161
Outstanding, weighted average grant date fair value (in dollars per share)	$ 53.20	$ 53.36	$ 49.48
Granted (in shares)	34,570	26,614	18,311
Granted, weighted average grant date fair value (in dollars per share)	$ 49.83	$ 52.03	$ 55.00
Forfeited (in shares)	(3,428)	(439)	0
Forfeited, weighted average grant date fair value (in dollars per share)	$ 52.13	$ 52.66
Vested (in shares)	(11,699)	(13,209)	(15,395)
Vested, weighted average grant date fair value (in dollars per share)	$ 52.83	$ 51.23	$ 48.47
Non-vested balance (in shares)	62,486	43,043	30,077
Outstanding, weighted average grant date fair value (in dollars per share)	$ 51.46	$ 53.20	$ 53.36
The 2012 Director Stock Incentive Plan [Member]
Non-vested balance (in shares)	14,920	9,402	11,200
Granted (in shares)	18,000	12,500	6,000
Granted, weighted average grant date fair value (in dollars per share)	$ 49.85	$ 52.00	$ 56.63
Forfeited (in shares)	0	0	0
Vested (in shares)	(9,048)	(6,982)	(7,798)
Non-vested balance (in shares)	23,872	14,920	9,402
The 2012 Omnibus Stock Incentive Plan [Member]
Non-vested balance (in shares)	28,123	20,675	15,961
Granted (in shares)	16,570	14,114	12,311
Forfeited (in shares)	(3,428)	(439)	0
Vested (in shares)	(2,651)	(6,227)	(7,597)
Non-vested balance (in shares)	38,614	28,123	20,675