Note 7 - Stock Plans - Summary of Weighted Average Fair Value and Vesting of Restricted Stock Grants (Details) - Restricted Stock [Member] - $ / shares	3 Months Ended
	Mar. 31, 2023		Mar. 31, 2022
Granted, awards (in shares)	35,734		34,520
Shares granted, weighted average grant date fair value (in dollars per share)	$ 49.43		$ 49.85
The 2012 Director Stock Incentive Plan [Member]
Granted, awards (in shares)	0	[1]	18,000
Shares granted, weighted average grant date fair value (in dollars per share)	$ 0		$ 49.85
The 2012 Omnibus Stock Incentive Plan [Member] | Award Date One [Member]
Granted, awards (in shares)	18,000	[2]	16,520	[1]
Shares granted, weighted average grant date fair value (in dollars per share)	$ 49.43		$ 49.85
The 2012 Omnibus Stock Incentive Plan [Member] | Award Date Two [Member]
Granted, awards (in shares)	17,684			[2]
Shares granted, weighted average grant date fair value (in dollars per share)	$ 49.43
The 2012 Omnibus Stock Incentive Plan [Member] | Award Date Three [Member]
Granted, awards (in shares)	50			[3]
Shares granted, weighted average grant date fair value (in dollars per share)	$ 49.43

[1] Vest after 3 years – 33% each year

[2] Vest fully after 3 years

[3] Vest after 1 year