Note 7 - Stock Plans - Summary of Weighted Average Fair Value and Vesting of Restricted Stock Grants (Details) - Restricted Stock [Member] - $ / shares		9 Months Ended
		Sep. 30, 2022	Sep. 30, 2021
Granted, awards (in shares)		34,570	26,614
Shares granted, weighted average grant date fair value (in dollars per share)		$ 49.83	$ 52.03
The 2012 Director Stock Incentive Plan [Member]
Granted, awards (in shares)	[1]	18,000	12,500
Shares granted, weighted average grant date fair value (in dollars per share)		$ 49.85	$ 52.00
The 2012 Omnibus Stock Incentive Plan [Member] | Award Date One [Member]
Granted, awards (in shares)	[2]	16,520	13,552
Shares granted, weighted average grant date fair value (in dollars per share)		$ 49.85	$ 52.00
The 2012 Omnibus Stock Incentive Plan [Member] | Award Date Two [Member]
Granted, awards (in shares)		50	50	[3]
Shares granted, weighted average grant date fair value (in dollars per share)		$ 35.91	$ 58.17
The 2012 Omnibus Stock Incentive Plan [Member] | Award Date Three [Member]
Granted, awards (in shares)		0	36	[2]
Shares granted, weighted average grant date fair value (in dollars per share)			$ 58.17
The 2012 Omnibus Stock Incentive Plan [Member] | Award Date Four [Member]
Granted, awards (in shares)	[1]	0	476
Shares granted, weighted average grant date fair value (in dollars per share)			$ 52.62

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

[2] Vest fully after 3 years

[3] Vest after 1 year