Note 10 - Stock-based Compensation - Shares Authorized Under Stock Option Plan (Details)	12 Months Ended
	Dec. 31, 2021 $ / shares shares
Number of shares outstanding (in shares) | shares	624,531
Weighted average remaining contractual life (Year)	3 years 2 months 26 days
Weighted average exercise price (in dollars per share)	$ 2.13
Price Range 1 [Member]
Exercise price, lower range (in dollars per share)	1.00
Exercise price, upper range (in dollars per share)	$ 1.50
Number of shares outstanding (in shares) | shares	26,428
Weighted average remaining contractual life (Year)	1 year 18 days
Weighted average exercise price (in dollars per share)	$ 1.38
Price Range 2 [Member]
Exercise price, lower range (in dollars per share)	1.51
Exercise price, upper range (in dollars per share)	$ 2.00
Number of shares outstanding (in shares) | shares	290,760
Weighted average remaining contractual life (Year)	3 years 3 months 7 days
Weighted average exercise price (in dollars per share)	$ 1.87
Price Range 3 [Member]
Exercise price, lower range (in dollars per share)	2.01
Exercise price, upper range (in dollars per share)	$ 2.50
Number of shares outstanding (in shares) | shares	265,775
Weighted average remaining contractual life (Year)	3 years 4 months 6 days
Weighted average exercise price (in dollars per share)	$ 2.06
Price Range 4 [Member]
Exercise price, lower range (in dollars per share)	2.51
Exercise price, upper range (in dollars per share)	$ 8.60
Number of shares outstanding (in shares) | shares	41,568
Weighted average remaining contractual life (Year)	3 years 9 months
Weighted average exercise price (in dollars per share)	$ 4.86