Note 13 - Summary of Stock Options - Summary of Options Outstanding and Exercisable (Details)	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Options outstanding, number (in shares) | shares	986,399
Options outstanding, weighted average exercise price (in dollars per share)	$ 19.10
Options outstanding, weighted average remaining contractual term (Year)	8 years 328 days
Options exercisable, number exercisable (in shares) | shares	245,445
Options exercisable, weighted average exercise price (in dollars per share)	$ 45.09
Range One [Member]
Exercise price range, lower limit (in dollars per share)	4.45
Exercise price range, upper limit (in dollars per share)	$ 8.91
Options outstanding, number (in shares) | shares	967,288
Options outstanding, weighted average exercise price (in dollars per share)	$ 8.32
Options outstanding, weighted average remaining contractual term (Year)	8 years 328 days
Options exercisable, number exercisable (in shares) | shares	238,900
Options exercisable, weighted average exercise price (in dollars per share)	$ 8.69
Range Two [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)	9 years 73 days
Options exercisable, number exercisable (in shares) | shares	3,750
Options exercisable, weighted average exercise price (in dollars per share)	$ 13.60
Range Three [Member]
Exercise price range, lower limit (in dollars per share)	380
Exercise price range, upper limit (in dollars per share)	$ 580
Options outstanding, number (in shares) | shares	125
Options outstanding, weighted average exercise price (in dollars per share)	$ 552
Options outstanding, weighted average remaining contractual term (Year)	8 years 146 days
Options exercisable, number exercisable (in shares) | shares	113
Options exercisable, weighted average exercise price (in dollars per share)	$ 567.61
Range Four [Member]
Exercise price range, lower limit (in dollars per share)	1,000
Exercise price range, upper limit (in dollars per share)	$ 1,970
Options outstanding, number (in shares) | shares	1,954
Options outstanding, weighted average exercise price (in dollars per share)	$ 1,426.46
Options outstanding, weighted average remaining contractual term (Year)	7 years 219 days
Options exercisable, number exercisable (in shares) | shares	1,334
Options exercisable, weighted average exercise price (in dollars per share)	$ 1,437.21
Range Five [Member]
Exercise price range, lower limit (in dollars per share)	2,020
Exercise price range, upper limit (in dollars per share)	$ 2,830
Options outstanding, number (in shares) | shares	74
Options outstanding, weighted average exercise price (in dollars per share)	$ 2,501.22
Options outstanding, weighted average remaining contractual term (Year)	7 years
Options exercisable, number exercisable (in shares) | shares	53
Options exercisable, weighted average exercise price (in dollars per share)	$ 2,520.19
Range Six [Member]
Exercise price range, lower limit (in dollars per share)	3,110
Exercise price range, upper limit (in dollars per share)	$ 3,580
Options outstanding, number (in shares) | shares	189
Options outstanding, weighted average exercise price (in dollars per share)	$ 3,439.26
Options outstanding, weighted average remaining contractual term (Year)	7 years 219 days
Options exercisable, number exercisable (in shares) | shares	156
Options exercisable, weighted average exercise price (in dollars per share)	$ 3,455.90
Range Seven [Member]
Exercise price range, lower limit (in dollars per share)	4,360
Exercise price range, upper limit (in dollars per share)	$ 4,970
Options outstanding, number (in shares) | shares	619
Options outstanding, weighted average exercise price (in dollars per share)	$ 4,549.77
Options outstanding, weighted average remaining contractual term (Year)	6 years 73 days
Options exercisable, number exercisable (in shares) | shares	510
Options exercisable, weighted average exercise price (in dollars per share)	$ 4,554.04
Range Eight [Member]
Exercise price range, lower limit (in dollars per share)	5,010
Exercise price range, upper limit (in dollars per share)	$ 5,670
Options outstanding, number (in shares) | shares	300
Options outstanding, weighted average exercise price (in dollars per share)	$ 5,366
Options outstanding, weighted average remaining contractual term (Year)	6 years 73 days
Options exercisable, number exercisable (in shares) | shares	285
Options exercisable, weighted average exercise price (in dollars per share)	$ 5,356.84
Range Nine [Member]
Exercise price range, lower limit (in dollars per share)	6,000
Exercise price range, upper limit (in dollars per share)	$ 6,000
Options outstanding, number (in shares) | shares	138
Options outstanding, weighted average exercise price (in dollars per share)	$ 6,000
Options outstanding, weighted average remaining contractual term (Year)	5 years
Options exercisable, number exercisable (in shares) | shares	138
Options exercisable, weighted average exercise price (in dollars per share)	$ 6,000
Range Ten [Member]
Exercise price range, lower limit (in dollars per share)	7,140
Exercise price range, upper limit (in dollars per share)	$ 7,920
Options outstanding, number (in shares) | shares	200
Options outstanding, weighted average exercise price (in dollars per share)	$ 7,679.20
Options outstanding, weighted average remaining contractual term (Year)	4 years 36 days
Options exercisable, number exercisable (in shares) | shares	194
Options exercisable, weighted average exercise price (in dollars per share)	$ 7,676.29
Range Eleven [Member]
Exercise price range, lower limit (in dollars per share)	9,920
Exercise price range, upper limit (in dollars per share)	$ 9,920
Options outstanding, number (in shares) | shares	12
Options outstanding, weighted average exercise price (in dollars per share)	$ 9,920
Options outstanding, weighted average remaining contractual term (Year)	2 years 36 days
Options exercisable, number exercisable (in shares) | shares	12
Options exercisable, weighted average exercise price (in dollars per share)	$ 9,920