Note 15 - Stock-based Compensation - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Options, Outstanding, Number of Shares (in shares)	4,361,872
Options, Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 10.49
Options, Outstanding, Weighted Average Remaining Contractual Term (Year)	5 years 7 months 28 days	6 years 18 days
Options, Granted, Number of Shares (in shares)	1,490,266	3,005,964	623,272
Options, Grants in Period, Weighted Average Exercise Price (in dollars per share)	$ 4.06
Options, Forfeited, Number of Shares (in shares)	(285,391)
Options, Forfeitures in Period, Weighted Average Exercise Price (in dollars per share)	$ 8.10
Options, Cancelled, Number of Shares (in shares)	(610,287)
Options, Expirations in Period, Weighted Average Exercise Price (in dollars per share)	$ 30.32
Options, Exercised, Number of Shares (in shares)	(315,800)
Options, Exercises in Period, Weighted Average Exercise Price (in dollars per share)	$ 0.67
Options, Outstanding, Number of Shares (in shares)	4,640,660	4,361,872
Options, Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.64	$ 10.49