Note 2 - Summary of Significant Accounting Policies - Anti-dilutive Securities (Details) - shares		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Anti-dilutive securities (in shares)		8,367,074	6,869,441
Convertible Debt Securities [Member]
Anti-dilutive securities (in shares)		6,683,646	4,840,556
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)		1,281,327	1,616,227
Share-based Payment Arrangement, Option [Member]
Anti-dilutive securities (in shares)		291,807	302,364

[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.