Note 11 - Stock-based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2023	Dec. 31, 2022
Options, Outstanding, Number of Shares (in shares)	7,584,967
Options, Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 4.22
Options, Outstanding, Weighted Average Remaining Contractual Term (Year)	5 years 4 months 2 days	5 years 3 months 21 days
Options, Granted, Number of Shares (in shares)	3,047,615
Options, Grants in Period, Weighted Average Exercise Price (in dollars per share)	$ 0.71
Options, Exercised, Number of Shares (in shares)	(13,300)
Options, Exercises in Period, Weighted Average Exercise Price (in dollars per share)	$ 0.38
Options, Cancelled, Number of Shares (in shares)	(16,762)
Options, Expirations in Period, Weighted Average Exercise Price (in dollars per share)	$ 27.89
Options, Forfeited, Number of Shares (in shares)	(106)
Options, Forfeitures in Period, Weighted Average Exercise Price (in dollars per share)	$ 15.86
Options, Outstanding, Number of Shares (in shares)	10,602,414	7,584,967
Outstanding at June 30, 2023 (in dollars per share)	$ 3.18	$ 4.22
Options, Outstanding, Aggregate Intrinsic Value	$ 0.2
Options, Vested and Expected to Vest, Exercisable, Number of Shares (in shares)	10,028,804
Options, Vested and Expected to Vest, Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 3.32
Options, Vested and Expected to Vest, Exercisable, Weighted Average Remaining Contractual Term (Year)	5 years 3 months 14 days
Options, Vested or Expected to Vest, Aggregate Intrinsic Value	$ 0.2
Options, Exercisable, Number of Shares (in shares)	5,411,149
Options, Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.31
Options, Exercisable, Weighted Average Remaining Contractual Term (Year)	4 years 6 months 29 days
Options, Exercisable, Aggregate Intrinsic Value	$ 0.2