Note 6 - Stockholders' Equity and Stock-based Compensation - Summary of Performance Option Activity (Details) - Performance Options [Member] - $ / shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Options balances, number of shares (in shares)	1,200,097
Options balances, weighted average exercise price (in dollars per share)	$ 13.11
Options balances, weighted average remaining life (Year)	7 years 7 days	8 years 5 months 8 days
Options granted, number of shares (in shares)	200,000
Options granted, weighted average exercise price (in dollars per share)	$ 5.32
Options exercised, number of shares (in shares)	0
Options exercised, weighted average exercise price (in dollars per share)	$ 0
Options canceled, number of shares (in shares)	(797,920)
Options canceled, weighted average exercise price (in dollars per share)	$ 13.32
Options expired, number of shares (in shares)	(81,875)
Options expired, weighted average exercise price (in dollars per share)	$ 11.28
Options balances, number of shares (in shares)	520,302	1,200,097
Options balances, weighted average exercise price (in dollars per share)	$ 10.08	$ 13.11
Options exercisable, number of shares (in shares)	248,861
Options exercisable, weighted average exercise price (in dollars per share)	$ 12.25
Options exercisable, weighted average remaining life (Year)	4 years 11 months 1 day