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Note 7 - Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Mar. 31, 2016
The 2019 Stock Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Vested, Number of Shares (in shares)	3.8
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number (in shares)	5,610,000		4,694,000
Share-Based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount	$ 8.9
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	1 year 8 months 12 days
The 2019 Stock Plan [Member] \| Restricted Stock [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	243,850	60,300
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)	$ 3.6	$ 13.75
Inducement Equity Plan Options [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares)				100,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number (in shares)	0