Note 8 - Derivative Warrant Liability - Schedule of Common Stock on Warrants Exercised (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Issuance of common stock upon exercise of warrants (in shares)	300,911
Proceeds from the exercise of warrants	$ 1,263,766	$ 3,429,000	$ 12,298,000
Series A Warrants [Member]
Issuance of common stock upon exercise of warrants (in shares)	251
Proceeds from the exercise of warrants	$ 1,054
Series K Warrants [Member]
Issuance of common stock upon exercise of warrants (in shares)	300,660
Proceeds from the exercise of warrants	$ 1,262,712