Note 1 - Nature of Operations (Details Textual) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended		6 Months Ended	12 Months Ended
	Dec. 15, 2021	Dec. 22, 2020	Mar. 19, 2020	Feb. 28, 2021	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 09, 2020	Jun. 16, 2020	Mar. 31, 2020
Retained Earnings (Accumulated Deficit), Ending Balance					$ (157,392)	$ (157,392)	$ (180,405)	$ (157,392)
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.0001				$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Proceeds from Issuance of Private Placement	$ 16,740		$ 20,300
Proceeds from Warrant Exercises							$ 903	$ 0
Gain (Loss) on Disposition of Stock in Subsidiary							$ (567)	$ (2,526)
Maximum [Member]
Percentage of Operating Revenue of Disposed Subsidiaries of Total Revenue							15.00%
December 2020 Public Offering Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)		5,625,000			5,625,000	5,625,000		5,625,000
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)		$ 2.50			$ 2.50	$ 2.50		$ 2.50
Warrants and Rights Outstanding, Term (Year)		5 years			5 years	5 years		5 years
Class of Warrant or Right, Exercised During Period (in shares)				361,200
Class of Warrant or Right, Exercised During Period, Exercise Price (in dollars per share)				$ 2.50
Proceeds from Warrant Exercises				$ 903
Series A Preferred Stock [Member]
Preferred Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.0001		$ 0.0001
Proceeds from Issuance of Private Placement	$ 4,514		$ 8,063
Shares Issued, Price Per Share (in dollars per share)							$ 1.29				$ 2.47
Common Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)								4,245,256
Proceeds from Issuance of Private Placement	12,074		$ 4,052
The 2021 Private Placement [Member]
Proceeds from Issuance of Private Placement	16,999						$ 16,740	$ 0
Stock Issued, Costs	$ 259
The 2021 Private Placement [Member] | Series A Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)	3,790,755
Preferred Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.0001
Convertible Preferred Stock, Shares Issued upon Conversion (in shares)	3,790,755
The 2021 Private Placement [Member] | Common Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)	9,808,418
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.0001
December 2020 Public Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)		11,250,000			11,250,000
Common Stock, Par or Stated Value Per Share (in dollars per share)		$ 0.0001
Shares Issued, Price Per Share (in dollars per share)		$ 2.00
Proceeds from Issuance or Sale of Equity, Total		$ 22,500
Equity Purchase Agreement [Member] | Lincoln Park [Member]
Stock Issued During Period, Shares, New Issues (in shares)						3,037,087	0
Common Stock, Par or Stated Value Per Share (in dollars per share)										$ 0.0001
Shares Issued, Price Per Share (in dollars per share)					$ 2.97	$ 2.97		$ 2.97
Equity Purchase Agreement, Maximum Offering Amount										$ 31,000
Equity Purchase Agreement, Maximum Shares Issuable (in shares)										7,763,411
Equity Agreement, Maximum Percentage of Stock Outstanding										19.99%
Equity Agreement, Minimum Average Purchase Price (in dollars per share)										$ 3.9755
Maximum Percentage of Outstanding Stock, Beneficial Ownership										9.99%
Stock Issued During Period, Shares, Commitment Fee (in shares)						209,566
Stock Issued During Period, Value, Commitment Fee						$ 620
Deferred Offering Costs					$ 123	$ 123		$ 123
Proceeds From Issuance of Common Stock, Gross							$ 9,010
Amortization of Deferred Charges, Total							520
Common Stock, Shares Issued as Commitment Shares, Value							$ 620