Note 12 - Summary of Stock Options - Summary of Options Outstanding and Exercisable (Details)	9 Months Ended
	Sep. 30, 2020 $ / shares shares
Options outstanding, number (in shares) | shares	9,755,454
Options outstanding, weighted average exercise price (in dollars per share)	$ 1.96
Options outstanding, weighted average remaining contractual term (Year)	9 years 36 days
Options exercisable, number exercisable (in shares) | shares	1,969,073
Options exercisable, weighted average exercise price (in dollars per share)	$ 5.19
Range One [Member]
Exercise price range, lower limit (in dollars per share)	0.52
Exercise price range, upper limit (in dollars per share)	$ 0.89
Options outstanding, number (in shares) | shares	9,563,606
Options outstanding, weighted average exercise price (in dollars per share)	$ 0.85
Options outstanding, weighted average remaining contractual term (Year)	9 years 36 days
Options exercisable, number exercisable (in shares) | shares	1,918,010
Options exercisable, weighted average exercise price (in dollars per share)	$ 0.87
Range Two [Member]
Exercise price range, lower limit (in dollars per share)	1.09
Exercise price range, upper limit (in dollars per share)	$ 1.36
Options outstanding, number (in shares) | shares	155,000
Options outstanding, weighted average exercise price (in dollars per share)	$ 1.26
Options outstanding, weighted average remaining contractual term (Year)	9 years 146 days
Options exercisable, number exercisable (in shares) | shares	25,000
Options exercisable, weighted average exercise price (in dollars per share)	$ 1.36
Range Three [Member]
Exercise price range, lower limit (in dollars per share)	38
Exercise price range, upper limit (in dollars per share)	$ 58
Options outstanding, number (in shares) | shares	1,250
Options outstanding, weighted average exercise price (in dollars per share)	$ 55.20
Options outstanding, weighted average remaining contractual term (Year)	8 years 255 days
Options exercisable, number exercisable (in shares) | shares	1,115
Options exercisable, weighted average exercise price (in dollars per share)	$ 56.99
Range Four [Member]
Exercise price range, lower limit (in dollars per share)	100
Exercise price range, upper limit (in dollars per share)	$ 197
Options outstanding, number (in shares) | shares	19,996
Options outstanding, weighted average exercise price (in dollars per share)	$ 142.17
Options outstanding, weighted average remaining contractual term (Year)	8 years
Options exercisable, number exercisable (in shares) | shares	11,956
Options exercisable, weighted average exercise price (in dollars per share)	$ 144.84
Range Five [Member]
Exercise price range, lower limit (in dollars per share)	202
Exercise price range, upper limit (in dollars per share)	$ 283
Options outstanding, number (in shares) | shares	725
Options outstanding, weighted average exercise price (in dollars per share)	$ 250.69
Options outstanding, weighted average remaining contractual term (Year)	7 years 109 days
Options exercisable, number exercisable (in shares) | shares	451
Options exercisable, weighted average exercise price (in dollars per share)	$ 253.26
Range Six [Member]
Exercise price range, lower limit (in dollars per share)	311
Exercise price range, upper limit (in dollars per share)	$ 358
Options outstanding, number (in shares) | shares	1,875
Options outstanding, weighted average exercise price (in dollars per share)	$ 343.99
Options outstanding, weighted average remaining contractual term (Year)	7 years 328 days
Options exercisable, number exercisable (in shares) | shares	1,505
Options exercisable, weighted average exercise price (in dollars per share)	$ 346.28
Range Seven [Member]
Exercise price range, lower limit (in dollars per share)	430
Exercise price range, upper limit (in dollars per share)	$ 497
Options outstanding, number (in shares) | shares	6,443
Options outstanding, weighted average exercise price (in dollars per share)	$ 454.44
Options outstanding, weighted average remaining contractual term (Year)	6 years 146 days
Options exercisable, number exercisable (in shares) | shares	4,935
Options exercisable, weighted average exercise price (in dollars per share)	$ 455.06
Range Eight [Member]
Exercise price range, lower limit (in dollars per share)	501
Exercise price range, upper limit (in dollars per share)	$ 567
Options outstanding, number (in shares) | shares	3,139
Options outstanding, weighted average exercise price (in dollars per share)	$ 537.25
Options outstanding, weighted average remaining contractual term (Year)	6 years 73 days
Options exercisable, number exercisable (in shares) | shares	2,777
Options exercisable, weighted average exercise price (in dollars per share)	$ 536.54
Range Nine [Member]
Exercise price range, lower limit (in dollars per share)	600
Exercise price range, upper limit (in dollars per share)	$ 661
Options outstanding, number (in shares) | shares	1,379
Options outstanding, weighted average exercise price (in dollars per share)	$ 601.64
Options outstanding, weighted average remaining contractual term (Year)	5 years 36 days
Options exercisable, number exercisable (in shares) | shares	1,379
Options exercisable, weighted average exercise price (in dollars per share)	$ 601.64
Range Ten [Member]
Exercise price range, lower limit (in dollars per share)	700
Exercise price range, upper limit (in dollars per share)	$ 792
Options outstanding, number (in shares) | shares	1,937
Options outstanding, weighted average exercise price (in dollars per share)	$ 767.72
Options outstanding, weighted average remaining contractual term (Year)	6 years 36 days
Options exercisable, number exercisable (in shares) | shares	1,841
Options exercisable, weighted average exercise price (in dollars per share)	$ 767.15
Range Eleven [Member]
Exercise price range, lower limit (in dollars per share)	992
Exercise price range, upper limit (in dollars per share)	$ 992
Options outstanding, number (in shares) | shares	104
Options outstanding, weighted average exercise price (in dollars per share)	$ 992
Options outstanding, weighted average remaining contractual term (Year)	2 years 109 days
Options exercisable, number exercisable (in shares) | shares	104
Options exercisable, weighted average exercise price (in dollars per share)	$ 992