Note 2 - Summary of Significant Accounting Policies - Calculation for Basic and Diluted Earnings Per Share (Details) - shares		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Anti-dilutive securities (in shares)		6,340,367	5,237,147
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)		4,030,600	3,725,782
Employee Stock Option [Member]
Anti-dilutive securities (in shares)		1,206,410	334,190
Restricted Stock Units (RSUs) [Member]
Anti-dilutive securities (in shares)		416	74,234

[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.