Note 2 - Summary of Significant Accounting Policies - Anti-dilutive Securities (Details) - shares		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019
Anti-dilutive securities (in shares)		8,996,967	7,720,081
Convertible Debt Securities [Member]
Anti-dilutive securities (in shares)		6,988,334	6,013,667
Vested Series A Warrants [Member]
Anti-dilutive securities (in shares)		40,441	40,441
Unvested Series A Warrants [Member]
Anti-dilutive securities (in shares)	[1]	69,853	69,853
Warrant, Other [Member]
Anti-dilutive securities (in shares)		1,006,190	1,300,091
Share-based Payment Arrangement, Option [Member]
Anti-dilutive securities (in shares)		892,149	296,029

[1] The unvested Series A warrants were subject to vesting based upon the amount of funds actually received by the Company in the second close of the August 2015 financing which never occurred. The warrants will remain outstanding but unvested until they expire in February 2021.