Note 1 - Organization and Description of Business (Details Textual) $ / shares in Units, $ in Thousands				3 Months Ended	12 Months Ended
	Feb. 08, 2024 USD ($)	Aug. 11, 2023 $ / shares	May 09, 2023 USD ($)	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($) $ / shares	Dec. 31, 2022 USD ($) $ / shares	Dec. 22, 2021 $ / shares
Net Income (Loss) Attributable to Parent					$ (74,564)	$ (196,292)
Net Cash Provided by (Used in) Operating Activities					(13,388)	(17,477)
Cash and Cash Equivalents, at Carrying Value					20,023	43,574
Retained Earnings (Accumulated Deficit)					$ (699,815)	$ (625,251)
Number of Restructuring Plans					2
Common Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares		$ 0.0001			$ 0.0001	$ 0.0001	$ 0.0001
Restructuring Charges					$ 1,632	$ 0
Employee Severance [Member]
Restructuring Charges			$ 1,600		$ 915
Employee Severance [Member] | Subsequent Event [Member]
Restructuring Charges	$ 600			$ 600
Employee Severance [Member] | Employees [Member]
Restructuring and Related Cost, Number of Positions Eliminated			50
Employee Severance [Member] | Employees [Member] | Subsequent Event [Member]
Restructuring and Related Cost, Number of Positions Eliminated	21
Employee Severance [Member] | Contractors [Member]
Restructuring and Related Cost, Number of Positions Eliminated			15
Employee Severance [Member] | Contractors [Member] | Subsequent Event [Member]
Restructuring and Related Cost, Number of Positions Eliminated	27
Reverse Stock Split [Member] | Minimum [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio		2
Reverse Stock Split [Member] | Maximum [Member]
Stockholders' Equity Note, Stock Split, Conversion Ratio		30