Note 14 - Stock-based Compensation - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Options, Outstanding, Number of Shares (in shares)	1,830,958
Options, Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 30.71
Options, Outstanding, Weighted Average Remaining Contractual Term (Year)	6 years 18 days	7 years 4 months 9 days
Options, Granted, Number of Shares (in shares)	3,005,964	623,272
Options, Grants in Period, Weighted Average Exercise Price (in dollars per share)	$ 0.54
Options, Forfeited, Number of Shares (in shares)	(293,102)
Options, Forfeitures in Period, Weighted Average Exercise Price (in dollars per share)	$ 19.08
Options, Cancelled, Number of Shares (in shares)	(181,948)
Options, Expirations in Period, Weighted Average Exercise Price (in dollars per share)	$ 35.57
Options, Exercised, Number of Shares (in shares)	0
Options, Exercises in Period, Weighted Average Exercise Price (in dollars per share)	$ 0
Options, Outstanding, Number of Shares (in shares)	4,361,872	1,830,958
Options, Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 10.49	$ 30.71