Note 11 - Stock-based Compensation - Stock Option Activity (Details) - $ / shares	6 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2020
Options, Outstanding, Number of Shares (in shares)	4,640,660
Options, Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 6.64
Options, Outstanding, Weighted Average Remaining Contractual Term (Year)	5 years 8 months 15 days	5 years 7 months 28 days
Options, Granted, Number of Shares (in shares)	2,555,396
Options, Grants in Period, Weighted Average Exercise Price (in dollars per share)	$ 0.77
Options, Forfeited, Number of Shares (in shares)	(23,047)
Options, Forfeitures in Period, Weighted Average Exercise Price (in dollars per share)	$ 3.22
Options, Cancelled, Number of Shares (in shares)	(16,983)
Options, Expirations in Period, Weighted Average Exercise Price (in dollars per share)	$ 33.27
Options, Exercised, Number of Shares (in shares)	(43,453)
Options, Exercises in Period, Weighted Average Exercise Price (in dollars per share)	$ 0.41
Options, Outstanding, Number of Shares (in shares)	7,112,573
Options, Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 4.52