Note 12 - Stockholders' Equity (Details Textual)		12 Months Ended		62 Months Ended	72 Months Ended
	Feb. 13, 2018 USD ($) shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2013 USD ($)	Feb. 13, 2018 USD ($) shares	Dec. 31, 2014 USD ($)	Dec. 31, 2012 USD ($)	Mar. 02, 2020 USD ($)	Dec. 31, 2019 $ / shares shares	Sep. 30, 2019 USD ($)	Apr. 11, 2019 USD ($)	Mar. 20, 2019 USD ($)
Preferred Stock, Shares Authorized (in shares) | shares		5,000,000						5,000,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares		$ 0.0001						$ 0.0001
Preferred Stock, Shares Outstanding, Ending Balance (in shares) | shares		0						0
Common Stock, Number of Votes Per Share		1
Dividends, Common Stock, Total		$ 0
Warrants in Connection with March 2019 Offering [Member]
Warrants and Rights Outstanding											$ 100,000
The March 2020 Offering Placement Agent Warrants [Member]
Warrants and Rights Outstanding							$ 453,000
Warrants in Connection With the April 2019 Offering [Member]
Warrants and Rights Outstanding										$ 333,000
Underwriter Warrants, September 2019 [Member]
Warrants and Rights Outstanding									$ 497,000
First Set of Warrants Expiring September 2024 [Member]
Warrant Exercise Price to be Entitled to Receive Cash Consideration, Fundamental Transaction (in dollars per share) | $ / shares		$ 0.30
Second Set of Warrants Expiring April 2024 [Member]
Warrant Exercise Price to be Entitled to Receive Cash Consideration, Fundamental Transaction (in dollars per share) | $ / shares		0.375
First Set of Warrants Expiring April 2024 [Member]
Warrant Exercise Price to be Entitled to Receive Cash Consideration, Fundamental Transaction (in dollars per share) | $ / shares		1.10
Warrants Expiring March 2025 [Member]
Warrant Exercise Price to be Entitled to Receive Cash Consideration, Fundamental Transaction (in dollars per share) | $ / shares		2.50
Warrants Expiring February 2025 [Member]
Warrant Exercise Price to be Entitled to Receive Cash Consideration, Fundamental Transaction (in dollars per share) | $ / shares		$ 3.125
Conversion From Series C Preferred Stock to Common Stock [Member]
Conversion of Stock, Shares Issued (in shares) | shares	696,028
Accumulated and Undeclared Dividends, Shares Issued Upon Conversion (in shares) | shares	253,851			253,851
Conversion From Series B Preferred Stock to Common Stock [Member]
Conversion of Stock, Shares Issued (in shares) | shares	599,259
Accumulated and Undeclared Dividends, Shares Issued Upon Conversion (in shares) | shares	265,340			265,340
Conversion From Series A Preferred Stock to Common Stock [Member]
Conversion of Stock, Shares Issued (in shares) | shares	104,065
Series C Convertible Preferred Stock [Member]
Proceeds from Issuance of Convertible Preferred Stock			$ 20,000,000
Preferred Stock, Dividend Rate, Percentage			8.00%
Dividends, Total				$ 0
Accumulated and Undeclared Dividends	$ 7,300,000			7,300,000
Pre-merger Accumulated and Undeclared Dividends	188,000			188,000
Series B Convertible Preferred Stock [Member]
Proceeds from Issuance of Convertible Preferred Stock					$ 16,000,000
Preferred Stock, Dividend Rate, Percentage					8.00%
Accumulated and Undeclared Dividends	7,600,000			7,600,000
Pre-merger Accumulated and Undeclared Dividends	$ 151,000			$ 151,000
Series A Convertible Preferred Stock [Member]
Proceeds from Issuance of Convertible Preferred Stock						$ 2,900,000
Dividends, Total						$ 0