Note 8 - Stock-based Compensation Expense - Summary of Stock Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Balance (in shares)	67,000	417,000
Balance, grant date weighted-average exercise price (in dollars per share)	$ 2.72	$ 2.79
Balance, weighted average remaining contractual life (Year)	4 years 9 months 29 days	3 years 3 months 29 days	1 year 7 months 9 days
Granted (in shares)	50,000	6,000
Granted, grant date weighted-average exercise price (in dollars per share)	$ 2.72	$ 2.92
Granted, weighted average remaining contractual life (Year)	7 years	7 years
Exercised (in shares)	(4,000)	(22,000)
Exercised, grant date weighted-average exercise price (in dollars per share)	$ 2.29	$ 2.65
Forfeited (in shares)	(18,000)	(334,000)
Forfeited, grant date weighted-average exercise price (in dollars per share)	$ 2.64	$ 2.81
Balance, aggregate intrinsic value	$ 25,000	$ 0
Balance (in shares)	95,000	67,000	417,000
Balance, grant date weighted-average exercise price (in dollars per share)	$ 2.76	$ 2.72	$ 2.79
Exercisable (in shares)	38,000	58,000
Exercisable, grant date weighted-average exercise price (in dollars per share)	$ 2.79	$ 2.72
Exercisable, weighted average remaining contractual life (Year)	2 years 4 months 17 days
Minimum [Member]
Exercisable, weighted average remaining contractual life (Year)		2 years 11 months 15 days