Note 3 - Stockholders' Equity, Stock Options and Warrants - Schedule of Listing of Stock Options and Warrants (Details)	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Shares, options (in shares) | shares	3,090,578
Shares, warrants (in shares) | shares	2,860,052
Minimum [Member]
Price, options (in dollars per share)	$ 0.97
Exercise price per share (in dollars per share)	0
Maximum [Member]
Price, options (in dollars per share)	596.25
Exercise price per share (in dollars per share)	$ 609.38
Warrants 2013 [Member]
Shares, warrants (in shares) | shares	1,126
Warrants 2013 [Member] | Minimum [Member]
Exercise price per share (in dollars per share)	$ 337.50
Warrants 2013 [Member] | Maximum [Member]
Exercise price per share (in dollars per share)	$ 371.25
Warrants 2014 [Member]
Shares, warrants (in shares) | shares	6,455
Warrants 2014 [Member] | Minimum [Member]
Exercise price per share (in dollars per share)	$ 243.75
Warrants 2014 [Member] | Maximum [Member]
Exercise price per share (in dollars per share)	$ 609.38
Warrants 2015 [Member]
Shares, warrants (in shares) | shares	94,151
Warrants 2015 [Member] | Minimum [Member]
Exercise price per share (in dollars per share)	$ 0
Warrants 2015 [Member] | Maximum [Member]
Exercise price per share (in dollars per share)	$ 243.75
Warrants 2016 [Member]
Shares, warrants (in shares) | shares	756,999
Exercise price per share (in dollars per share)	$ 4.46
Warrants 2017 [Member]
Shares, warrants (in shares) | shares	1,082,946
Warrants 2017 [Member] | Minimum [Member]
Exercise price per share (in dollars per share)	$ 1.07
Warrants 2017 [Member] | Maximum [Member]
Exercise price per share (in dollars per share)	$ 2.25
Warrants 2018 [Member]
Shares, warrants (in shares) | shares	918,375
Exercise price per share (in dollars per share)	$ 1
Stock Options 2011 [Member]
Shares, options (in shares) | shares	173
Price, options (in dollars per share)	$ 281.25
Stock Options 2012 [Member]
Shares, options (in shares) | shares	1,841
Stock Options 2012 [Member] | Minimum [Member]
Price, options (in dollars per share)	$ 131.25
Stock Options 2012 [Member] | Maximum [Member]
Price, options (in dollars per share)	$ 150
Stock Options 2013 [Member]
Shares, options (in shares) | shares	1,553
Stock Options 2013 [Member] | Minimum [Member]
Price, options (in dollars per share)	$ 148.125
Stock Options 2013 [Member] | Maximum [Member]
Price, options (in dollars per share)	$ 596.25
Stock Options 2014 [Member]
Shares, options (in shares) | shares	836
Stock Options 2014 [Member] | Minimum [Member]
Price, options (in dollars per share)	$ 162.50
Stock Options 2014 [Member] | Maximum [Member]
Price, options (in dollars per share)	$ 431.25
Stock Options 2015 [Member]
Shares, options (in shares) | shares	4,088
Stock Options 2015 [Member] | Minimum [Member]
Price, options (in dollars per share)	$ 65.75
Stock Options 2015 [Member] | Maximum [Member]
Price, options (in dollars per share)	$ 86.25
Stock Options 2016 [Member]
Shares, options (in shares) | shares	144,422
Stock Options 2016 [Member] | Minimum [Member]
Price, options (in dollars per share)	$ 2.25
Stock Options 2016 [Member] | Maximum [Member]
Price, options (in dollars per share)	$ 5.13
Stock Options 2017 [Member]
Shares, options (in shares) | shares	2,612,070
Stock Options 2017 [Member] | Minimum [Member]
Price, options (in dollars per share)	$ 1.01
Stock Options 2017 [Member] | Maximum [Member]
Price, options (in dollars per share)	$ 2.10
Stock Options 2018 [Member]
Shares, options (in shares) | shares	325,595
Stock Options 2018 [Member] | Minimum [Member]
Price, options (in dollars per share)	$ 0.97
Stock Options 2018 [Member] | Maximum [Member]
Price, options (in dollars per share)	$ 1.35