Note 11 - Stock-based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended	12 Months Ended
	Sep. 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 1 month 6 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)	(21,116)
Options, Expirations in Period, Weighted Average Exercise Price (in dollars per share)	$ 25.79
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)	10,598,060	7,584,967
Outstanding at September 30, 2023 (in dollars per share)	$ 3.17	$ 4.22
Options, Outstanding, Aggregate Intrinsic Value	$ 0
Options, Vested and Expected to Vest, Exercisable, Number of Shares (in shares)	10,132,754
Options, Vested and Expected to Vest, Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 3.29
Options, Vested and Expected to Vest, Exercisable, Weighted Average Remaining Contractual Term (Year)	5 years 18 days
Options, Vested or Expected to Vest, Aggregate Intrinsic Value	$ 0
Options, Exercisable, Number of Shares (in shares)	5,591,291
Options, Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 5.15
Options, Exercisable, Weighted Average Remaining Contractual Term (Year)	4 years 4 months 13 days
Options, Exercisable, Aggregate Intrinsic Value	$ 0