Note 13 - Warrants - Summary of Warrant Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Warrants outstanding (in shares)	1,487,958	421,015
Warrants outstanding (in dollars per share)	$ 9.39	$ 5,888
Warrants issued in connection with equity transactions (in shares)	9,231,628	1,147,595
Warrants issued in connection with equity transactions (in dollars per share)	$ 3.46	$ 2.03
Warrants exercised (in shares)	(7,617,147)	(17,857)
Warrants exercised (in dollars per share)	$ 2.89	$ 0.14
Warrants expired (in shares)	(44,037)	(62,795)
Warrants expired (in dollars per share)	$ 174.58	$ 209.23
Warrants outstanding (in shares)	3,058,402	1,487,958
Warrants outstanding (in dollars per share)	$ 5.29	$ 9.39
Aggregate intrinsic value of outstanding warrants	$ 37,143
Weighted average remaining contractual terms (Year)	3 years 182 days