Note 10 - Stockholders' Equity (Details Textual) - USD ($)					12 Months Ended
	May 30, 2022	Mar. 22, 2021	Jan. 08, 2021	Jan. 06, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 21, 2022	May 19, 2014
Number of Shares Authorized to Issue (in shares)					185,000,000
Common Stock, Shares Authorized (in shares)					175,000,000	175,000,000
Common Stock, Par or Stated Value Per Share (in dollars per share)					$ 0.18	$ 0.18
Preferred Stock, Shares Authorized (in shares)					10,000,000	10,000,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share)					$ 0.001	$ 0.001
Preferred Stock, Shares Issued (in shares)					1,000	1,000
Stockholder Rights Agreement, Number of Preferred Stock Right Distributed for Each Share of Common Stock (in shares)								1
Stockholder Rights Agreement, Acquiring Person, Percentage of Ownership								15.00%
Stockholder Rights Agreement, Acquiring Person, Additional Percentage of Ownership								2.00%
Stockholder Rights Agreement, Initial Exercise Price of Each Right (in dollars per share)								$ 15.00
Stockholder Rights Agreement, Share Price (in dollars per share)								$ 30.00
Proceeds From Issuance of Common Stock and Warrants, Net of Issuance Costs					$ 0	$ 69,668,000
Consummate a Business Combination, Percentage of Acquired Outstanding Shares					50.00%
Consummate a Business Combination, Percentage of Aggregate Ordinary Voting Power					50.00%
Class of Warrant or Right, Outstanding (in shares)					21,515
Class of Warrant or Right, Exercised During Period (in shares)					0	37,451,000
Proceeds from Warrant Exercises					$ 0	$ 43,818,000
Stock Issued During Period, Shares, Warrant Exercised (in shares)						37,451,000
Conversion of Series B Convertible Preferred Stock into Common Stock [Member]
Conversion of Stock, Shares Converted (in shares)					0	39.000
Conversion of Stock, Shares Issued (in shares)						11,000
Convertible Preferred Stock, Shares Issued upon Conversion (in shares)						284,000
The 2021 Financing Transaction Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)		0.75
Warrants and Rights Outstanding, Term (Year)		4 years 6 months
The 2020 Liability Warrants [Member]
Warrants and Rights Outstanding, Term (Year)					4 years
Warrants Associated with 2020 Offering Consisting of Common Stock and Warrants [Member]
Warrants and Rights Outstanding, Term (Year)					4 years 6 months
The 2020 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)					$ 1.055
Warrants Exercisable, Ownership Percentage of Company’s Shares Allowed							4.99%
Common Stock, Convertible, Ownership Percentage of Company’s Shares Allowed							9.99%
Class of Warrant or Right, Outstanding (in shares)					4,500
The 2018 Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)					$ 1.00
Class of Warrant or Right, Outstanding (in shares)					6,490
Class of Warrant or Right, Warrants Expired (in shares)	762
Class of Warrant or Right, Expirations in Period, Exercise Price (in dollars per share)	$ 4.05
The 2021 Financing Transaction [Member]
Common Stock, Par or Stated Value Per Share (in dollars per share)		$ 0.18		$ 0.18
Stock Issued During Period, Shares, New Issues (in shares)		17,361,000		23,850,000
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)		13,021,000
Issuance of Common Stock and Warrants, Combined Purchase Price Per Share (in dollars per share)				$ 1.055
Proceeds From Issuance of Common Stock and Warrants, Net of Issuance Costs		$ 46,400,000	$ 23,300,000
Shares Issued, Price Per Share (in dollars per share)		$ 2.88
The 2021 Financing Transaction [Member] | The 2021 Financing Transaction Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)				17,888,000
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)				0.75
Warrants and Rights Outstanding, Term (Year)				4 years 6 months
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)				$ 1.055
Series A Junior Participating Preferred Stock [Member]
Preferred Stock, Shares Authorized (in shares)					750,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share)					$ 0.001
Preferred Stock, Shares Issued (in shares)					0	0
Series A Convertible Preferred Stock [Member]
Preferred Stock, Shares Authorized (in shares)					4,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share)					$ 0.001
Preferred Stock, Shares Issued (in shares)					0	0
Series B Convertible Preferred Stock [Member]
Preferred Stock, Shares Authorized (in shares)					25,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share)					$ 0.001
Preferred Stock, Convertible, Conversion Price (in dollars per share)					$ 3.52
Series C Convertible Preferred Stock [Member]
Preferred Stock, Shares Authorized (in shares)					20,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share)					$ 0.001
Preferred Stock, Shares Issued (in shares)					0	0
Stated Value per Share					$ 1,000
Preferred Stock, Convertible, Ownership Percentage of Company’s Shares Allowed					9.99%