Note 2 - Summary of Significant Accounting Policies - Anti-dilutive Securities (Details) - shares		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018
Anti-dilutive securities (in shares)		70,558,337	6,340,367
Convertible Debt Securities [Member]
Anti-dilutive securities (in shares)		50,967,211
Vested Series A Warrants [Member]
Anti-dilutive securities (in shares)		404,412	404,412
Unvested Series A Warrants [Member]
Anti-dilutive securities (in shares)	[1]	698,529	698,529
Warrant, Other [Member]
Anti-dilutive securities (in shares)		15,578,847	4,030,600
Share-based Payment Arrangement, Option [Member]
Anti-dilutive securities (in shares)		2,909,338	1,206,410
Restricted Stock Units (RSUs) [Member]
Anti-dilutive securities (in shares)			416

[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.