Note 9 - Stockholders' Equity (Details Textual) - USD ($)				3 Months Ended			6 Months Ended
	Mar. 22, 2021	Jan. 08, 2021	Jan. 06, 2021	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Number of Shares Authorized to Issue (in shares)				185,000,000			185,000,000
Common Stock, Shares Authorized (in shares)				175,000,000			175,000,000		175,000,000
Common Stock, Par or Stated Value Per Share (in dollars per share)				$ 0.18			$ 0.18		$ 0.18
Preferred Stock, Shares Authorized (in shares)				10,000,000			10,000,000		10,000,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share)				$ 0.001			$ 0.001		$ 0.001
Preferred Stock, Shares Issued, Total (in shares)				587			587		621
Proceeds From Issuance of Common Stock and Warrants, Net of Issuance Costs							$ 69,668,408	$ 0
Issuance of Common Stock and Warrants, Issuance Costs					$ 5,493,310
Class of Warrant or Right, Outstanding (in shares)				22,572,854			22,572,854
Proceeds from Warrant Exercises				$ 10,196,000		$ 0	$ 42,955,943	$ 0
Class of Warrant or Right, Exercised During Period (in shares)				5,091,000			37,155,000
Stock Issued During Period, Shares, Warrant Exercised (in shares)				5,091,000			37,155,000
Conversion of Series B Convertible Preferred Stock into Common Stock [Member]
Conversion of Stock, Shares Converted (in shares)				33		45	34
Conversion of Stock, Shares Issued (in shares)				9,377		12,786	9,662
The 2021 Financing Transaction Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)	13,020,825
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)				1			1
Warrants and Rights Outstanding, Term (Year)	4 years 6 months
Warrants and Rights Outstanding, Percent of Shares Sold Warrants May Call	75.00%
Warrants Exercisable, Ownership Percentage of Company’s Shares Allowed				4.99%			4.99%
Common Stock, Convertible, Ownership Percentage of Company’s Shares Allowed				9.99%			9.99%
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)	17,361,100		23,850,000
Issuance of Common Stock and Warrants, Combined Purchase Price Per Share (in dollars per share)			$ 1.055
Stock Issuance Costs, Commission Fee Percent	7.00%		7.00%
Maximum Stock Issuance Expenses to Reimburse Placement Agent	$ 45,000		$ 45,000
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
Issuance of Common Stock and Warrants, Issuance Costs	$ 70,000
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)			17,887,500
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			750,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share)				$ 0.001			$ 0.001
Preferred Stock, Shares Issued, Total (in shares)				0			0
Series A Convertible Preferred Stock [Member]
Preferred Stock, Shares Authorized (in shares)				4,000			4,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share)				$ 0.001			$ 0.001
Preferred Stock, Shares Issued, Total (in shares)				0			0
Series B Convertible Preferred Stock [Member]
Preferred Stock, Shares Authorized (in shares)				25,000			25,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share)				$ 0.001			$ 0.001
Series C Convertible Preferred Stock [Member]
Preferred Stock, Shares Authorized (in shares)				5,425			5,425
Preferred Stock, Par or Stated Value Per Share (in dollars per share)				$ 0.001			$ 0.001
Preferred Stock, Shares Issued, Total (in shares)				0			0