Note 12 - Summary of Stock Options - Summary of Options Outstanding and Exercisable (Details)	3 Months Ended
	Mar. 31, 2022 $ / shares shares
Options outstanding, number (in shares) | shares	4,110,009
Options outstanding, weighted average exercise price (in dollars per share)	$ 6.08
Options outstanding, weighted average remaining contractual term (Year)	9 years
Options exercisable, number exercisable (in shares) | shares	995,692
Options exercisable, weighted average exercise price (in dollars per share)	$ 15.65
Range One [Member]
Exercise price range, lower limit (in dollars per share)	1.26
Exercise price range, upper limit (in dollars per share)	$ 1.26
Options outstanding, number (in shares) | shares	941,000
Options outstanding, weighted average exercise price (in dollars per share)	$ 1.26
Options outstanding, weighted average remaining contractual term (Year)	9 years 9 months 18 days
Options exercisable, number exercisable (in shares) | shares	39,212
Options exercisable, weighted average exercise price (in dollars per share)	$ 1.26
Range Two [Member]
Exercise price range, lower limit (in dollars per share)	2.28
Exercise price range, upper limit (in dollars per share)	$ 2.96
Options outstanding, number (in shares) | shares	2,207,000
Options outstanding, weighted average exercise price (in dollars per share)	$ 2.73
Options outstanding, weighted average remaining contractual term (Year)	9 years 2 months 12 days
Options exercisable, number exercisable (in shares) | shares	387,341
Options exercisable, weighted average exercise price (in dollars per share)	$ 2.73
Range Three [Member]
Exercise price range, lower limit (in dollars per share)	3.06
Exercise price range, upper limit (in dollars per share)	$ 3.40
Options outstanding, number (in shares) | shares	10,000
Options outstanding, weighted average exercise price (in dollars per share)	$ 3.20
Options outstanding, weighted average remaining contractual term (Year)	9 years
Options exercisable, number exercisable (in shares) | shares	1,833
Options exercisable, weighted average exercise price (in dollars per share)	$ 3.26
Range Four [Member]
Exercise price range, lower limit (in dollars per share)	4.45
Exercise price range, upper limit (in dollars per share)	$ 4.80
Options outstanding, number (in shares) | shares	11,900
Options outstanding, weighted average exercise price (in dollars per share)	$ 4.72
Options outstanding, weighted average remaining contractual term (Year)	8 years 8 months 12 days
Options exercisable, number exercisable (in shares) | shares	3,832
Options exercisable, weighted average exercise price (in dollars per share)	$ 4.71
Range Five [Member]
Exercise price range, lower limit (in dollars per share)	5.10
Exercise price range, upper limit (in dollars per share)	$ 5.40
Options outstanding, number (in shares) | shares	88,000
Options outstanding, weighted average exercise price (in dollars per share)	$ 5.28
Options outstanding, weighted average remaining contractual term (Year)	8 years 6 months
Options exercisable, number exercisable (in shares) | shares	62,563
Options exercisable, weighted average exercise price (in dollars per share)	$ 5.34
Range Six [Member]
Exercise price range, lower limit (in dollars per share)	6.90
Exercise price range, upper limit (in dollars per share)	$ 6.90
Options outstanding, number (in shares) | shares	5,400
Options outstanding, weighted average exercise price (in dollars per share)	$ 6.90
Options outstanding, weighted average remaining contractual term (Year)	8 years
Options exercisable, number exercisable (in shares) | shares	2,700
Options exercisable, weighted average exercise price (in dollars per share)	$ 6.90
Range Seven [Member]
Exercise price range, lower limit (in dollars per share)	8.60
Exercise price range, upper limit (in dollars per share)	$ 8.91
Options outstanding, number (in shares) | shares	827,800
Options outstanding, weighted average exercise price (in dollars per share)	$ 8.69
Options outstanding, weighted average remaining contractual term (Year)	7 years 8 months 12 days
Options exercisable, number exercisable (in shares) | shares	481,974
Options exercisable, weighted average exercise price (in dollars per share)	$ 8.69
Range Eight [Member]
Exercise price range, lower limit (in dollars per share)	10.90
Exercise price range, upper limit (in dollars per share)	$ 13.60
Options outstanding, number (in shares) | shares	15,500
Options outstanding, weighted average exercise price (in dollars per share)	$ 12.64
Options outstanding, weighted average remaining contractual term (Year)	7 years 10 months 24 days
Options exercisable, number exercisable (in shares) | shares	12,865
Options exercisable, weighted average exercise price (in dollars per share)	$ 13.00
Range Nine [Member]
Exercise price range, lower limit (in dollars per share)	380.00
Exercise price range, upper limit (in dollars per share)	$ 9,920.00
Options outstanding, number (in shares) | shares	3,409
Options outstanding, weighted average exercise price (in dollars per share)	$ 2,878.01
Options outstanding, weighted average remaining contractual term (Year)	6 years
Options exercisable, number exercisable (in shares) | shares	3,372
Options exercisable, weighted average exercise price (in dollars per share)	$ 2,890.61