Note 7 - Stock-based Compensation - Summary of Stock Option Activity (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Dec. 31, 2020
Outstanding (in shares)	67,000	417,000	417,000
Outstanding, grant date weighted-average exercise price (in dollars per share)	$ 2.72	$ 2.79	$ 2.79
Outstanding, weighted average remaining contractual life (Year)		1 year 4 months 9 days	3 years 3 months 29 days	1 year 7 months 9 days
Outstanding, intrinsic value		$ 19,000		$ 2,000
Exercisable (in shares)	59,000	407,000
Exercisable, grant date weighted-average exercise price (in dollars per share)	$ 2.72	$ 2.80
Exercisable, weighted average remaining contractual life (Year)		1 year 3 months 7 days
Outstanding (in shares)	67,000	417,000	67,000	417,000
Outstanding, grant date weighted-average exercise price (in dollars per share)	$ 2.72	$ 2.79	$ 2.72	$ 2.79
Minimum [Member]
Outstanding, weighted average remaining contractual life (Year)	3 years 1 month 2 days
Exercisable, weighted average remaining contractual life (Year)	2 years 9 months 7 days
Maximum [Member]
Outstanding, intrinsic value	$ 4,000