Note 7 - Embedded Derivatives and Derivative Warrant Liabilities (Details Textual) $ / shares in Units, $ in Thousands		1 Months Ended				3 Months Ended				6 Months Ended				12 Months Ended
		Jan. 31, 2018 USD ($) shares	Oct. 31, 2017 $ / shares shares	Sep. 30, 2017 $ / shares shares	Jun. 30, 2017	Jun. 30, 2018 USD ($) $ / shares shares		Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) $ / shares shares		Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2011 $ / shares shares	Apr. 19, 2017	Feb. 28, 2017 shares	Feb. 17, 2017 shares	Sep. 13, 2016 shares	Apr. 01, 2016 shares	Dec. 11, 2015 shares	May 19, 2015 shares	Feb. 03, 2015 shares	Aug. 05, 2014 shares	Dec. 16, 2013 shares	Jul. 31, 2012
Embedded Derivative, Gain (Loss) on Embedded Derivative, Net, Total | $						$ (511)			$ (1,662)	$ 2,347			$ (1,662)
Class of Warrant or Right, Number of Securities Called by Warrants or Rights						58,902	[1]			58,902	[1]					855,378
Proceeds from Warrant Exercises | $										$ 1,263			$ 6
Class of Warrant or Right, Issued During Period														6
Class of Warrant or Right, Issued During Period, Exercise Price | $ / shares														$ 354
2013 Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights						2,789	[1]			2,789	[1]													3,551
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares						$ 85.05				$ 85.05
2014 Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights						974	[1]			974	[1]												2,500
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares						$ 65.50				$ 65.50
Series A Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights						320	[1]			320	[1]											5,542
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares						$ 3.80				$ 3.80
Class of Warrant or Right, Exercised During Period						251
Series B Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights							[1]				[1]											5,542
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares	[2]
Series C Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights						1,075	[1]			1,075	[1]										1,075
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares						$ 53.43				$ 53.43
Series D Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights						47	[1]			47	[1]									25,125
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares						$ 40				$ 40
Series E Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights							[1]				[1]									20,000
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares	[2]
Series F Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights						14,041	[1]			14,041	[1]								25,733
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares						$ 40				$ 40
Series H Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights							[1]				[1]								51,465
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares	[2]
Series G Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights							[1]				[1]								16,429
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares	[2]
Series I Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights						35,650	[1]			35,650	[1]							35,650
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares						$ 220				$ 220
Series J Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights							[1]				[1]							9,250
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares	[2]
Series K Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights						4,006	[1]			4,006	[1]						312,516
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares						$ 3.80				$ 3.80
Class of Warrant or Right, Exercised During Period						300,510
Series M Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights																	312,500
Warrants Issued to Purchase Additional Shares of Common Stock			74,250	197,250
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares				$ 12
Proceeds from Warrant Exercises | $								$ 1,000				$ 2,400
Series M Warrants [Member] | Minimum [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares			$ 12
Series M Warrants [Member] | Maximum [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares			$ 13
Series L Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights							[1]				[1]						28,500
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares	[2]
Series A and K Warrants [Member]
Proceeds from Warrant Exercises | $						$ 1,300
Class of Warrant or Right, Exercised During Period						300,761
Common Stock [Member]
Debt Conversion, Converted Instrument, Shares Issued		39,016
Convertible 2020 Notes [Member]
Debt Instrument, Interest Rate, Stated Percentage					12.00%				12.00%				12.00%		12.00%
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger					150.00%
Debt Instrument, Convertible, Threshold Consecutive Trading Days					10
Number of Embedded Derivative					1
Embedded Derivative, Fair Value of Embedded Derivative, Net, Total | $						$ 700		5,200		$ 700		5,200
Convertible 2020 Notes [Member] | Embedded Derivative, 2020 Convertible Notes [Member]
Embedded Derivative, Gain (Loss) on Embedded Derivative, Net, Total | $						$ 500				$ 2,300
Convertible 2022 Notes [Member]
Debt Instrument, Interest Rate, Stated Percentage																									7.50%
Embedded Derivative, Fair Value of Embedded Derivative, Net, Total | $								$ 0				$ 0
Debt Conversion, Original Debt, Amount | $		$ 500
Debt Conversion, Converted Instrument, Shares Issued		39,016

[1] This table does not include equity-classified warrants to purchase 6 shares of common stock issued in 2011, with strike price of $354 per share.

[2] Warrants have either been fully exercised and/or expired as of June 30, 2018.