Note 8 - Stock-based Compensation - Stock Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Outstanding at beginning of year, options (in shares)	484,500	747,500
Outstanding at beginning of year, weighted average exercise price (in dollars per share)	$ 3.57	$ 3.33
Granted, options (in shares)	0	0
Granted, option, weighted average exercise price (in dollars per share)	$ 0	$ 0
Exercised, options (in shares)	0	(183,000)
Exercised, option, weighted average exercise price (in dollars per share)	$ 0	$ 1.61
Expired or forfeited, options (in shares)	(50,000)	(80,000)
Expired or forfeited, option, weighted average exercise price (in dollars per share)	$ 8.16	$ 5.79
Outstanding at end of year, options (in shares)	434,500	484,500
Outstanding at end of year, weighted average exercise price (in dollars per share)	$ 3.05	$ 3.57
Exercisable, options (in shares)	434,500	484,500
Exercisable, option, weighted average exercise price (in dollars per share)	$ 3.05	$ 3.57
Weighted-Average Remaining Contractual Life (years) (Year)	3 years 29 days	3 years 8 months 12 days
Aggregate Intrinsic Value	$ 38	$ 488