Note 7 - Stock Option Plans and Stock-based Compensation - Shares Outstanding Under Option Plan (Details) - $ / shares	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Options outstanding (in shares)	146,698	65,471
Weighted average remaining contractual life (Year)	6 years 10 days
Shares exercisable (in shares)	65,471
Weighted average exercise price (in dollars per share)	$ 9.95
Range 1 [Member]
Options outstanding (in shares)	48,724
Weighted average remaining contractual life (Year)	1 year 1 month 6 days
Shares exercisable (in shares)	48,724
Weighted average exercise price (in dollars per share)	$ 11.89
Range 2 [Member]
Options outstanding (in shares)	16,747
Weighted average remaining contractual life (Year)	3 years 2 months 8 days
Shares exercisable (in shares)	16,747
Weighted average exercise price (in dollars per share)	$ 31.33
Range 3 [Member]
Options outstanding (in shares)	65,227
Weighted average remaining contractual life (Year)	9 years 6 months 14 days
Shares exercisable (in shares)	0
Weighted average exercise price (in dollars per share)	$ 4.30
Range 4 [Member]
Options outstanding (in shares)	16,000
Weighted average remaining contractual life (Year)	9 years 8 months 15 days
Shares exercisable (in shares)	0
Weighted average exercise price (in dollars per share)	$ 4.73