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Note 9 - Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Millions			12 Months Ended
	Aug. 26, 2021	Apr. 25, 2019	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2020	Dec. 31, 2021	Jul. 01, 2021	Mar. 31, 2016
Share Price (in dollars per share)			$ 5.24	$ 3.96
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number (in shares)			5,526,000	4,694,000
Share-Based Payment Arrangement, Expense			$ 7.7	$ 6.4
Share-Based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount			$ 7.3
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)			1 year 6 months
The 2019 Stock Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period (Year)		10 years
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares)							4,558,621
Share-Based Compensation Arrangement by Share-Based Payment Award, Percentage Increase in Shares Available for Issuance Based on Common stock Outstanding	4.00%
Share-Based Compensation Arrangement by Share-Based Payment Award, Measurement Input, Shares (in shares)	2,541,823
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)			244,000
Share Price (in dollars per share)			$ 3.6	$ 10.97
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number (in shares)			5,526,000	4,694,000		3,763,000
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)				89,000
The 2019 Stock Plan [Member] | Restricted Stock [Member] | Director [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)			244,000	89,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value (in dollars per share)			$ 3.75	$ 10.92
The 2019 Stock Plan [Member] | Share-Based Payment Arrangement, Employee [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercisable, Number (in shares)			1,300,000	1,300,000
The 2019 Stock Plan [Member] | Share-Based Payment Arrangement, Employee [Member] | Share-Based Payment Arrangement, Option [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period (Year)					10 years
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period (Year)					3 years
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

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