Note 7 - Stock-based Compensation - Summary of Stock Option Activity (Details) - USD ($)	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021	Dec. 31, 2020
Outstanding (in shares)		67,000		417,000	67,000	417,000	417,000
Outstanding, grant date weighted-average exercise price (in dollars per share)	$ 2.74	$ 2.72	$ 2.80	$ 2.79	$ 2.72	$ 2.79	$ 2.79
Outstanding, weighted average remaining contractual life (Year)				1 year 1 month 28 days			3 years 3 months 29 days	1 year 7 months 9 days
Exercised (in shares)					(2,000)	(22,000)
Exercised (in dollars per share)					$ 2.70	$ 2.65
Forfeited (in shares)					(7,000)	(7,000)
Forfeited (in dollars per share)					$ 2.58	$ 2.51
Outstanding, intrinsic value				$ 15,000				$ 2,000
Exercisable (in shares)	50,000		383,000		50,000	383,000
Exercisable, grant date weighted-average exercise price (in dollars per share)		2.74		$ 2.80
Exercisable, weighted average remaining contractual life (Year)				1 year 7 days
Granted (in shares)						6,000
Granted (in dollars per share)						$ 2.92
Granted (Year)						7 years
Outstanding (in shares)	58,000		394,000		58,000	394,000	67,000	417,000
Outstanding, grant date weighted-average exercise price (in dollars per share)		$ 2.74		$ 2.80			$ 2.72	$ 2.79
Minimum [Member]
Outstanding, weighted average remaining contractual life (Year)		3 years 3 months 14 days
Exercisable, weighted average remaining contractual life (Year)		2 years 11 months 26 days
Maximum [Member]
Outstanding, intrinsic value		$ 3,000