Note 10 - Warrant Liabilities (Details Textual)		3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 22, 2017 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) shares	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) shares	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 $ / shares shares	Oct. 26, 2016 $ / shares	Mar. 10, 2016 USD ($) $ / shares shares	Jul. 02, 2012 USD ($) $ / shares shares	Jun. 30, 2012 USD ($) $ / shares shares
Fair Value Adjustment of Warrants		$ (283,000)	$ 2,039,000	$ (8,000)	$ 889,000
Class of Warrant or Right, Outstanding | shares		10,066,809		10,066,809		10,066,809
Warrant [Member]
Derivative Liability, Noncurrent		$ 2,184,000		$ 2,184,000		$ 2,192,000
Warrants in Connection with Vissar MTA Agreement [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | shares	21,317,094						21,317,094				15,000,000
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares	$ 0.16						$ 0.16				$ 0.22
Derivative Liability, Noncurrent											$ 4,260,000
Class of Warrant or Right, Exercised During Period | shares	21,317,094
Stock Issued During Period, Shares, Warrants Exercised in Period | shares	4,241,386
Decrease in Warrant Liability, Warrants Exercised	$ 975,000
Fair Value Adjustment of Warrants		0	0	0	(553,000)
Warrants in Connection with Vissar MTA Agreement [Member] | Common Stock [Member]
Stock Issued During Period, Value, Warrants Exercised in Period	4,000
Warrants in Connection with Vissar MTA Agreement [Member] | Additional Paid-in Capital [Member]
Stock Issued During Period, Value, Warrants Exercised in Period	$ 971,000
July 2012 Private Placement Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | shares										18,750,000
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares						$ 0.17				$ 0.384
Stock Issued During Period, Shares, Warrants Exercised in Period | shares						7,457,902
Decrease in Warrant Liability, Warrants Exercised						$ 1,247,000
Fair Value Adjustment of Warrants		0	(1,059,000)	0	(663,000)
Class Of Warrant Or Right Exercised in Period | shares						10,540,750
Proceeds from Warrant Exercises						$ 712,000
July 2012 Private Placement Warrants [Member] | Warrant [Member]
Derivative Liability, Noncurrent										$ 5,053,000
Warrants in Connection with the 2016 Purchase Agreement [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights | shares									10,066,809
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares								$ 0.07	$ 0.07
Fair Value Adjustment of Warrants		$ (283)	$ 980,000	$ (8,000)	$ 779,000
Warrants in Connection with the 2016 Purchase Agreement [Member] | Measurement Input, Expected Term [Member]
Warrants and Rights Outstanding, Measurement Input		7.69		7.69
Warrants in Connection with the 2016 Purchase Agreement [Member] | Measurement Input, Price Volatility [Member]
Warrants and Rights Outstanding, Measurement Input		0.88		0.88
Warrants in Connection with the 2016 Purchase Agreement [Member] | Measurement Input, Risk Free Interest Rate [Member]
Warrants and Rights Outstanding, Measurement Input		0.029		0.029
Warrants in Connection with the 2016 Purchase Agreement [Member] | Measurement Input, Expected Dividend Rate [Member]
Warrants and Rights Outstanding, Measurement Input		0		0
Warrants in Connection with the 2016 Purchase Agreement [Member] | Warrant [Member]
Derivative Liability, Noncurrent		$ 2,184,000		$ 2,184,000					$ 760,000