Note 8 - Stock-based Compensation - Summary of Outstanding Stock Options by Exercise Price Range (Details)	12 Months Ended
	Dec. 31, 2021 $ / shares shares
Number of Options (in shares) | shares	434,500
Weighted- Average Remaining Contractual Life (Year)	3 years 1 month 6 days
Weighted-Average Exercise Price (in dollars per share)	$ 3.05
Range One [Member]
Lower Range Limit (in dollars per share)	0.96
Upper Range Limit (in dollars per share)	$ 1.27
Number of Options (in shares) | shares	88,000
Weighted- Average Remaining Contractual Life (Year)	5 years 10 months 24 days
Weighted-Average Exercise Price (in dollars per share)	$ 0.97
Range Two [Member]
Lower Range Limit (in dollars per share)	1.28
Upper Range Limit (in dollars per share)	$ 3.00
Number of Options (in shares) | shares	132,000
Weighted- Average Remaining Contractual Life (Year)	3 years 7 months 6 days
Weighted-Average Exercise Price (in dollars per share)	$ 2.26
Range Three [Member]
Lower Range Limit (in dollars per share)	3.01
Upper Range Limit (in dollars per share)	$ 4.54
Number of Options (in shares) | shares	120,000
Weighted- Average Remaining Contractual Life (Year)	1 year
Weighted-Average Exercise Price (in dollars per share)	$ 3.72
Range Four [Member]
Lower Range Limit (in dollars per share)	4.55
Upper Range Limit (in dollars per share)	$ 5.22
Number of Options (in shares) | shares	94,500
Weighted- Average Remaining Contractual Life (Year)	2 years 4 months 24 days
Weighted-Average Exercise Price (in dollars per share)	$ 5.22