Note 3 - Miscellaneous Financial Information (Details Textual)					1 Months Ended		12 Months Ended
		Jan. 19, 2021 USD ($) $ / shares shares	Aug. 25, 2020 USD ($) $ / shares shares	Jul. 06, 2020 USD ($) $ / shares shares	Sep. 30, 2021 USD ($)	Mar. 31, 2020	Dec. 31, 2021 USD ($) $ / shares shares		Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares		Jul. 06, 2025 $ / shares	Apr. 15, 2021 USD ($)	Aug. 31, 2020 shares	Jul. 31, 2020 shares
Proceeds from Issuance or Sale of Equity, Total | $				$ 16,100,000
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)							97,734			30,315,986
Stock Issued During Period, Shares, Upon Exercise of Warrants (in shares)									53,678,400
Proceeds from Warrant Exercises | $							$ 1,121,000		$ 17,082,000	$ 0
Class of Warrant or Right, Outstanding (in shares)							97,734
Proceeds from Issuance of Common Stock | $							$ 489,373,000		76,414,000	11,589,000
Restructuring Reserve, Ending Balance | $							0		0	0
Workforce Reduced at Luverne Facility [Member]
Restructuring and Related Cost, Number of Positions Eliminated						26
Workforce Reduced at Corporate Headquarters [Member]
Restructuring and Related Cost, Number of Positions Eliminated						4
Blocksize and Leaf Resources [Member]
Payments for Software, Total | $									100,000
Due to Related Parties, Total | $									$ 100,000
Related Party Transaction, Amounts of Transaction | $							0			$ 0
The 2021 Bonds [Member]
Debt Instrument, Face Amount | $													$ 68,155,000
Debt Instrument, Unamortized Premium, Total | $							600,000						800,000
Debt Issuance Costs, Net, Total | $							$ 2,300,000						$ 3,000,000.0
Series 1 Unit [Member]
Units Issued During Period (in shares)				20,896,666
Units Issued Price Per Unit (in dollars per share) | $ / shares				$ 0.60
Units Issued Common Share Per Unit (in shares)				1
Units Issued Warrant Per Unit (in shares)				1
Series 1 Unit [Member] | Forecast [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares												$ 0.60
Series 2 Unit [Member]
Units Issued During Period (in shares)				9,103,334
Units Issued Price Per Unit (in dollars per share) | $ / shares				$ 0.59
Series 2020C Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)			16,532,232											16,532,232
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)			1
Class of Warrant or Right, Issuance Price (in dollars per share) | $ / shares			$ 1.29
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares			$ 0.01
Stock Issued During Period, Shares, Upon Exercise of Warrants (in shares)							1,866,558		16,532,232
Proceeds from Warrant Exercises | $							$ 1,120,000		$ 165,000
Series 2020 B Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)				30,000,000											9,103,334
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)				1
Units Issued Warrant Per Unit (in shares)				1
Stock Issued During Period, Shares, Upon Exercise of Warrants (in shares)									9,103,334
Proceeds from Warrant Exercises | $									$ 91,000
Series 2020 B Warrants [Member] | Forecast [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares												$ 0.01
The Series 2020 A Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)							90,608	[1]		30,000,000	[1]				30,000,000
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares	[1]						$ 0.60
Warrants and Rights Outstanding, Term (Year)									5 years
Stock Issued During Period, Shares, Upon Exercise of Warrants (in shares)							1,866,558		28,042,834
Proceeds from Warrant Exercises | $							$ 1,100,000		$ 16,826,000
Class of Warrant or Right, Outstanding (in shares)							90,608
January 2021 Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)		43,750,000
Shares Issued, Price Per Share (in dollars per share) | $ / shares		$ 8.00
Proceeds from Issuance or Sale of Equity, Total | $		$ 321,700,000
August 2020 Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)			21,929,313
Shares Issued, Price Per Share (in dollars per share) | $ / shares			$ 1.30
Proceeds from Issuance or Sale of Equity, Total | $			$ 45,800,000
At-the-market Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)							24,420,579		3,518,121
Increase (Decrease) in At-the-Market Offering of Stock | $					$ 500,000,000
Proceeds from Issuance of Common Stock | $							$ 135,800,000		$ 8,400,000
Payments of Stock Issuance Costs | $							3,600,000		$ 200,000
Offering of Stock, Remaining Capacity, Value | $							$ 500,000,000

[1] The Series 2020-A Warrants are equity-classified warrants.