Note 3 - Stockholders' Equity, Stock Options and Warrants - Summary of Transactions for Stock Options and Warrants (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Options exercise price (in dollars per share)		$ 65.75
Number of Shares Outstanding (in shares)	2,764,983
Warrant [Member]
Number of Shares Outstanding (in shares)	871,101	323,099
Average Exercise Price Outstanding (in dollars per share)	$ 52.22	$ 128.40
Number of Shares Issued (in shares)	1,082,946	1,487,881
Average Exercise Price Issued (in dollars per share)	$ 1.49	$ 0.71
Number of Shares Expired (in shares)	(2,790)
Average Exercise Price Expired (in dollars per share)	$ 281.46
Number of Shares Exercised (in shares)		(939,879)
Average Exercise Price Exercised (in dollars per share)
Number of Shares Outstanding (in shares)	1,951,257	871,101
Average Exercise Price Outstanding (in dollars per share)	$ 23.74	$ 52.22
Employee Stock Option [Member]
Number of Shares Outstanding (in shares)	165,643	31,350
Average Exercise Price Outstanding (in dollars per share)	$ 11.22	$ 133.23
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	2,612,070	157,982
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 1.45	$ 3.14
Number of Shares Expired (in shares)	(12,730)	(22,377)
Average Exercise Price Expired (in dollars per share)	$ 10.39	$ 122.13
Number of Shares Exercised (in shares)		(1,312)
Options exercise price (in dollars per share)		$ 65.75
Number of Shares Outstanding (in shares)	2,764,983	165,643
Average Exercise Price Outstanding (in dollars per share)	$ 2	$ 11.22