Note 17 - Equity Offerings (Details Textual) - USD ($) $ / shares in Units, $ in Thousands						1 Months Ended	4 Months Ended	12 Months Ended
	Jan. 29, 2021	Jan. 12, 2021	Jul. 06, 2020	Mar. 10, 2020	Sep. 04, 2019	Jan. 31, 2021	Jun. 30, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	May 19, 2021	Oct. 09, 2020	Mar. 31, 2020	Feb. 24, 2020	Aug. 12, 2019	Apr. 28, 2017
Shares Issued, Price Per Share (in dollars per share)																$ 1.00
Convertible Preferred Stock Converted to Other Securities								$ (0)	$ 299	$ (0)
Proceeds from Issuance of Equity Net								0	13,478	0
Proceeds from Warrant Exercises								30,600
Stock Issued During Period, Value, New Issues								131,929	33,846	25,777
Proceeds from Issuance of Common Stock, Net								$ 131,929	$ 33,847	$ 25,777
Stock Issued During Period, Shares, Warrants Exercised (in shares)								45,317,101
Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)								0	0	0
Stock Issued During Period, Shares, Conversion of Convertible Securities (in shares)							7,900,000		(7,937,000)
Stock Issued During Period Shares Stock Options and Warrants Exercised (in shares)								0	0	0
Stock Issued During Period, Value, New Issues								$ 0	$ 0	$ 0
Common Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)								71,787,000	66,241,000	3,571,000
Stock Issued During Period, Shares, Conversion of Convertible Securities (in shares)									7,937,000
Stock Issued During Period Shares Stock Options and Warrants Exercised (in shares)								45,630,000	4,913,000	38,000
Stock Issued During Period, Value, New Issues								$ 72	$ 66	$ 4
Series C Warrants [Member]
Proceeds from Warrant Exercises									$ 3,300
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)				$ 0.68
Series D Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)				$ 0.68
Series B Warrant [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)									567,660
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)								$ 0.35					$ 0.35	$ 0.35		$ 13.00
Class of Warrant or Right, Outstanding (in shares)								567,660						3,638,780
The 2019 ATM Offering [Member]
Stock Offering Agreement, Maximum Share Value															$ 25,000
The 2020 ATM Offering [Member]
Stock Offering Agreement, Maximum Share Value												$ 40,000
The 2021 ATM Offering [Member]
Stock Offering Agreement, Maximum Share Value											$ 100,000
Public Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)	26,545,832		42,857,142
Shares Issued, Price Per Share (in dollars per share)	$ 3.00		$ 0.35
Proceeds from Issuance of Equity Net			$ 13,600	$ 13,500
Stock Issued During Period, Value, New Issues									$ 13,477
Proceeds from Issuance of Common Stock	$ 79,600					$ 73,400
Proceeds from Issuance of Common Stock, Net	$ 73,400
Public Offering [Member] | Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)									7,937,000
Stock Issued During Period, Value, New Issues									$ 79
Public Offering [Member] | Common Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)									14,122,000
Stock Issued During Period, Value, New Issues									$ 14
Public Offering [Member] | Series C Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)				3,308,823
Public Offering [Member] | Series D Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)				3,308,823
Public Offering [Member] | Class A Units [Member]
Stock Issued During Period, Shares, New Issues (in shares)				14,121,766
Shares Issued, Price Per Share (in dollars per share)				$ 0.68
Public Offering [Member] | Class B Units [Member]
Stock Issued During Period, Shares, New Issues (in shares)				7,937,057
Shares Issued, Price Per Share (in dollars per share)				$ 0.68
Registered Direct Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)		25,000,000
Shares Issued, Price Per Share (in dollars per share)		$ 1.25
Stock Issued During Period, Value, New Issues		$ 31,250
Proceeds from Issuance of Common Stock		$ 28,600				$ 28,600
Underwriting Agreement [Member]
Stock Issued During Period, Shares, New Issues (in shares)					2,153,846
Proceeds from Issuance of Common Stock					$ 18,800
Over-Allotment Option [Member]
Stock Issued During Period, Shares, New Issues (in shares)					323,077