Note 6 - Stockholders' Equity and Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended				6 Months Ended	12 Months Ended
	Apr. 30, 2023	Jan. 01, 2023	Jun. 09, 2022	Mar. 31, 2024	Dec. 31, 2023	May 31, 2021	Nov. 30, 2017	Jun. 15, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2017
Preferred Stock, Shares Authorized (in shares)					50,000,000				50,000,000	50,000,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share)					$ 0.001				$ 0.001	$ 0.001
Preferred Stock, Shares Outstanding, Ending Balance (in shares)					0				0	0
Common Stock, Shares Authorized (in shares)					500,000,000				500,000,000	500,000,000
Common Stock, Par or Stated Value Per Share (in dollars per share)					$ 0.001				$ 0.001	$ 0.001
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)					$ 0				$ 0	$ 2.05
Proceeds from Issuance of Common Stock									$ 0	$ 14,864
Class of Warrant or Right, Exercised During Period (in shares)									7,237,657
Proceeds from Warrant Exercises									$ 14,828	$ 26
Class of Warrant or Right, Outstanding (in shares)					0				0	7,303,832
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount					$ 9,700				$ 9,700
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)									4 years 2 months 8 days
Time-based Options [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period, Intrinsic Value									$ 900
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Intrinsic Value									$ 9,000	$ 2,300
Time-based Options [Member] | Share-Based Payment Arrangement, Tranche One [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage									25.00%
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period (Year)									1 year
Performance Options [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Intrinsic Value									$ 2,000	800
Market-based Options [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Intrinsic Value									$ 10,500	$ 0
The 2017 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)											1,500,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized (in shares)		1,200,000			1,375,000					1,188,657
Increase in Shares Available for Issuance, Threshold of Common Stock Outstanding, Number of Shares (in shares)											1,200,000
Increase in Shares Available for Issuance, Threshold of Common Stock Outstanding, Percent											4.00%
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)					231,763				231,763
The 2017 Inducement Equity Incentive 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)							1,000,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized (in shares)						1,000,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)					1,249,126				1,249,126
The 2017 Inducement Equity Incentive Plan [Member] | Subsequent Event [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized (in shares)				2,000,000
The 2017 Inducement Equity Incentive Plan [Member] | Share-Based Payment Arrangement, Tranche One [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage							25.00%
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period (Year)							1 year
The 2017 Inducement Equity Incentive Plan [Member] | Share-Based Payment Arrangement, Option [Member] | Maximum [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period (Year)							10 years
The 2017 Employee Stock Purchase Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares)											250,000
Increase in Shares Available for Issuance, Threshold of Common Stock Outstanding, Number of Shares (in shares)											450,000
Increase in Shares Available for Issuance, Threshold of Common Stock Outstanding, Percent											1.50%
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)					113,318				113,318
Stock Issued During Period, Shares, Employee Stock Purchase Plans (in shares)									347,681	188,097
Rights Offering Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)			1
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)			$ 2.05		$ 2.05				$ 2.05
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)					7,317,072				7,317,072
Class of Warrants or Rights, Redemption Price Per Share (in dollars per share)					$ 0.01				$ 0.01
Class of Warrant or Right, Period of Written Notice for Exercise (Day)									30 days
Class of Warrant or Right, Percentage Required for Redemption					200.00%				200.00%
Class of Warrant or Right, Exercise, Consecutive Trading Days (Day)									20 days
Class of Warrant or Right, Exercised During Period (in shares)								7,250,897	66,175
Proceeds from Warrant Exercises								$ 14,900
Class of Warrant or Right, Outstanding (in shares)					0				0
Loan Agreement [Member]
Debt Instrument, Decrease, Forgiveness	$ 65,000
Private Placement [Member] | Robert W. Duggan [Member]
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.001
Stock Issued During Period, Shares, New Issues (in shares)	10,022,937
Shares Issued, Price Per Share (in dollars per share)	$ 6.51
Rights Offering [Member]
Common Stock, Par or Stated Value Per Share (in dollars per share)			$ 0.001
Stock Issued During Period, Shares, New Issues (in shares)			7,317,072
Shares Issued, Price Per Share (in dollars per share)			$ 2.05
Equity Offering, Units, Sale of Units (in shares)			7,317,072
Number of Shares Per Unit Issued (in shares)			1
Number of Warrants Per Unit (in shares)			1
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)			7,317,072
Proceeds from Issuance of Common Stock			$ 15,000
Class of Warrants or Rights, Redemption Price Per Share (in dollars per share)			$ 0.01
Rights Offering [Member] | Board of Directors Chairman [Member]
Investment Owned, Percent of Net Assets			56.00%
Rights Offering [Member] | Robert W. Duggan [Member]
Common Stock, Par or Stated Value Per Share (in dollars per share)			$ 0.001
Shares Issued, Price Per Share (in dollars per share)			$ 2.05
Equity Offering, Units, Sale of Units (in shares)			7,317,072
Number of Shares Per Unit Issued (in shares)			1
Number of Warrants Per Unit (in shares)			1
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)			1
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)			$ 2.05
Investment Owned, Percent of Net Assets			56.00%