Note 12 - Summary of Stock Options - Summary of Options Outstanding and Exercisable (Details)	9 Months Ended
	Sep. 30, 2021 $ / shares shares
Options outstanding, number (in shares) | shares	3,195,742
Options outstanding, weighted average exercise price (in dollars per share)	$ 7.52
Options outstanding, weighted average remaining contractual term (Year)	9 years 3 months 18 days
Options exercisable, number exercisable (in shares) | shares	581,757
Options exercisable, weighted average exercise price (in dollars per share)	$ 23.17
Range One [Member]
Exercise price range, upper limit (in dollars per share)	$ 2.96
Options outstanding, number (in shares) | shares	2,224,354
Options outstanding, weighted average exercise price (in dollars per share)	$ 2.73
Options outstanding, weighted average remaining contractual term (Year)	9 years 8 months 12 days
Options exercisable, number exercisable (in shares) | shares	130,533
Options exercisable, weighted average exercise price (in dollars per share)	$ 2.73
Range Two [Member]
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 6 months
Options exercisable, number exercisable (in shares) | shares	0
Options exercisable, weighted average exercise price (in dollars per share)	$ 0
Range Three [Member]
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)	9 years 2 months 12 days
Options exercisable, number exercisable (in shares) | shares	1,219
Options exercisable, weighted average exercise price (in dollars per share)	$ 4.80
Range Four [Member]
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)	9 years
Options exercisable, number exercisable (in shares) | shares	50,875
Options exercisable, weighted average exercise price (in dollars per share)	$ 5.40
Range Five [Member]
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 6 months
Options exercisable, number exercisable (in shares) | shares	2,026
Options exercisable, weighted average exercise price (in dollars per share)	$ 6.90
Range Six [Member]
Exercise price range, upper limit (in dollars per share)	$ 8.91
Options outstanding, number (in shares) | shares	837,150
Options outstanding, weighted average exercise price (in dollars per share)	$ 8.69
Options outstanding, weighted average remaining contractual term (Year)	8 years 1 month 6 days
Options exercisable, number exercisable (in shares) | shares	384,272
Options exercisable, weighted average exercise price (in dollars per share)	$ 8.69
Range Seven [Member]
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)	8 years 4 months 24 days
Options exercisable, number exercisable (in shares) | shares	9,678
Options exercisable, weighted average exercise price (in dollars per share)	$ 12.99
Range Eight [Member]
Exercise price range, upper limit (in dollars per share)	$ 9,920.00
Options outstanding, number (in shares) | shares	3,438
Options outstanding, weighted average exercise price (in dollars per share)	$ 2,876.47
Options outstanding, weighted average remaining contractual term (Year)	6 years 6 months
Options exercisable, number exercisable (in shares) | shares	3,154
Options exercisable, weighted average exercise price (in dollars per share)	$ 2,968.91