Note 6 - Stockholders' Equity and Stock-based Compensation - Summary of Stock Option Activity (Details) - The 2015 Plan, 2017 Plan and Inducement Plan [Member] - $ / shares	3 Months Ended	12 Months Ended
	Mar. 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 8 months 8 days	7 years 9 months 10 days
Options granted, number of shares (in shares)	639,000
Options granted, weighted average exercise price (in dollars per share)	$ 9
Options exercised, number of shares (in shares)	(3,000)
Options exercised, weighted average exercise price (in dollars per share)	$ 2.92
Options canceled, number of shares (in shares)	(4,125)
Options canceled, weighted average exercise price (in dollars per share)	$ 6.65
Options expired, number of shares (in shares)	(1,500)
Options expired, weighted average exercise price (in dollars per share)	$ 17.01
Options balances, number of shares (in shares)	10,096,411	9,466,036
Options balances, weighted average exercise price (in dollars per share)	$ 9.01	$ 9.01
Options exercisable, number of shares (in shares)	4,021,494
Options exercisable, weighted average exercise price (in dollars per share)	$ 13.58
Options exercisable, weighted average remaining life (Year)	5 years 4 months 28 days