Note 6 - Stockholders' Equity and Stock-based Compensation - Summary of Stock Option Activity (Details) - The 2015 Plan, 2017 Plan and Inducement Plan [Member] - $ / shares	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Options balances, number of shares (in shares)	9,466,036
Options balances, weighted average exercise price (in dollars per share)	$ 9.01
Options balances, weighted average remaining life (Year)	7 years 1 month 9 days	7 years 9 months 10 days
Options granted, number of shares (in shares)	3,018,643
Options granted, weighted average exercise price (in dollars per share)	$ 10.38
Options exercised, number of shares (in shares)	(160,847)
Options exercised, weighted average exercise price (in dollars per share)	$ 5.41
Options canceled, number of shares (in shares)	(1,308,542)
Options canceled, weighted average exercise price (in dollars per share)	$ 7.51
Options expired, number of shares (in shares)	(35,958)
Options expired, weighted average exercise price (in dollars per share)	$ 19.82
Options balances, number of shares (in shares)	10,979,332	9,466,036
Options balances, weighted average exercise price (in dollars per share)	$ 9.59	$ 9.01
Options exercisable, number of shares (in shares)	4,525,945
Options exercisable, weighted average exercise price (in dollars per share)	$ 12.74
Options exercisable, weighted average remaining life (Year)	4 years 11 months 23 days