Note 12 - Summary of Stock Options - Summary of Options Outstanding and Exercisable (Details)	12 Months Ended
	Dec. 31, 2019 $ / shares shares
Options outstanding, number (in shares) | shares	10,087,678
Options outstanding, weighted average exercise price (in dollars per share)	$ 2.22
Options outstanding, weighted average remaining contractual term (Year)	9 years 328 days
Options exercisable, number exercisable (in shares) | shares	222,582
Options exercisable, weighted average exercise price (in dollars per share)	$ 41.49
Range One [Member]
Exercise price range, lower limit (in dollars per share)	0.86
Exercise price range, upper limit (in dollars per share)	$ 0.89
Options outstanding, number (in shares) | shares	10,042,500
Options outstanding, weighted average exercise price (in dollars per share)	$ 0.87
Options outstanding, weighted average remaining contractual term (Year)	9 years 328 days
Options exercisable, number exercisable (in shares) | shares	198,312
Options exercisable, weighted average exercise price (in dollars per share)	$ 0.87
Range Two [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	1,650
Options outstanding, weighted average exercise price (in dollars per share)	$ 55.42
Options outstanding, weighted average remaining contractual term (Year)	9 years 146 days
Options exercisable, number exercisable (in shares) | shares
Options exercisable, weighted average exercise price (in dollars per share)
Range Three [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	22,385
Options outstanding, weighted average exercise price (in dollars per share)	$ 140.23
Options outstanding, weighted average remaining contractual term (Year)	8 years 36 days
Options exercisable, number exercisable (in shares) | shares	9,141
Options exercisable, weighted average exercise price (in dollars per share)	$ 144.93
Range Four [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	775
Options outstanding, weighted average exercise price (in dollars per share)	$ 252.06
Options outstanding, weighted average remaining contractual term (Year)	8 years
Options exercisable, number exercisable (in shares) | shares	355
Options exercisable, weighted average exercise price (in dollars per share)	$ 255.75
Range Five [Member]
Exercise price range, lower limit (in dollars per share)	311
Exercise price range, upper limit (in dollars per share)	$ 382
Options outstanding, number (in shares) | shares	3,833
Options outstanding, weighted average exercise price (in dollars per share)	$ 355.39
Options outstanding, weighted average remaining contractual term (Year)	6 years
Options exercisable, number exercisable (in shares) | shares	2,423
Options exercisable, weighted average exercise price (in dollars per share)	$ 362.12
Range Six [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	7,870
Options outstanding, weighted average exercise price (in dollars per share)	$ 453.47
Options outstanding, weighted average remaining contractual term (Year)	6 years 146 days
Options exercisable, number exercisable (in shares) | shares	5,066
Options exercisable, weighted average exercise price (in dollars per share)	$ 454.44
Range Seven [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	4,215
Options outstanding, weighted average exercise price (in dollars per share)	$ 536.47
Options outstanding, weighted average remaining contractual term (Year)	5 years 255 days
Options exercisable, number exercisable (in shares) | shares	3,258
Options exercisable, weighted average exercise price (in dollars per share)	$ 535.73
Range Eight [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	2,372
Options outstanding, weighted average exercise price (in dollars per share)	$ 601.29
Options outstanding, weighted average remaining contractual term (Year)	3 years 219 days
Options exercisable, number exercisable (in shares) | shares	2,352
Options exercisable, weighted average exercise price (in dollars per share)	$ 600.78
Range Nine [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	1,974
Options outstanding, weighted average exercise price (in dollars per share)	$ 768.12
Options outstanding, weighted average remaining contractual term (Year)	6 years 255 days
Options exercisable, number exercisable (in shares) | shares	1,571
Options exercisable, weighted average exercise price (in dollars per share)	$ 768.19
Range Ten [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)	3 years 36 days
Options exercisable, number exercisable (in shares) | shares	104
Options exercisable, weighted average exercise price (in dollars per share)	$ 992