Note 1 - The Company and Basis of Presentation (Details Textual) - USD ($)					1 Months Ended					11 Months Ended	12 Months Ended
	Nov. 12, 2019	Aug. 16, 2019	Feb. 12, 2018	Nov. 08, 2017	Dec. 31, 2019	Nov. 30, 2019	Aug. 31, 2019	Dec. 31, 2018	Feb. 28, 2018	Nov. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Shares Issued, Price Per Share													$ 2.56
Class of Warrant or Right, Number of Securities Called by Warrants or Rights					24,737,618			6,408			24,737,618	6,408
Debt Conversion, Converted Instrument, Amount											$ 35,529,000
Proceeds from Issuance of Common Stock											16,274,000	53,792,000
Retained Earnings (Accumulated Deficit), Ending Balance					$ (197,911,000)			$ (155,385,000)			(197,911,000)	(155,385,000)
Cash and Cash Equivalents, at Carrying Value, Ending Balance					13,308,000			$ 29,523,000			13,308,000	29,523,000		$ 20,730,000
Working Capital					$ 15,883,000						15,883,000
Net Cash Provided by (Used in) Operating Activities, Total											$ (31,236,000)	$ (43,090,000)
Conversion of Term Loan with CRG Into Stock and Warrants [Member]
Debt Conversion, Original Debt, Amount	$ 28,981,000
Debt Conversion, Converted Instrument, Amount	$ 31,300,000
Conversion of Term Loan with CRG Into Series B Convertible Preferred Stock [Member]
Debt Conversion, Converted Instrument, Shares Issued	31,300
Series A Convertible Preferred Stock Into Common Stock [Member]
Conversion of Stock, Shares Converted					3,021,237	600,000
Series B Convertible Preferred Stock Into Common Stock [Member] | Minimum [Member]
Conversion of Stock, Conversion Rate	$ 1.53
Series B Convertible Preferred Stock Into Common Stock [Member] | Maximum [Member]
Conversion of Stock, Conversion Rate	$ 1.836
Series A Preferred Stock [Member]
Convertible Preferred Stock, Shares Issued upon Conversion					1	1				1	1
Preferred Stock, Shares Outstanding, Ending Balance					1,852,173			0			1,852,173	0
Series A Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right						1				1
Class of Warrant or Right, Exercise Price of Warrants or Rights					$ 1.55	$ 1.55				$ 1.55	$ 1.55
Warrants and Rights Outstanding, Term						1 year				1 year
Class of Warrant or Right, Number of Securities Called by Warrants or Rights					7,419,353	7,419,353				7,419,353	7,419,353
Series B Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right						1				1
Class of Warrant or Right, Exercise Price of Warrants or Rights					$ 1.55	$ 1.55				$ 1.55	$ 1.55
Warrants and Rights Outstanding, Term						5 years				5 years
Class of Warrant or Right, Number of Securities Called by Warrants or Rights					7,419,353	7,419,353				7,419,353	7,419,353
Warrants Issued Upon Conversion of Term Loan with CRG [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights					$ 1.84						$ 1.84
Warrants and Rights Outstanding, Term	5 years
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	9,893,776				9,893,776						9,893,776
Class of Warrants and Rights Outstanding, Exercise Price Percentage of Conversion Rate	120.00%
Class A Units [Member] | Series A Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right						1				1
Class of Warrant or Right, Exercise Price of Warrants or Rights						$ 1.55				$ 1.55
Warrants and Rights Outstanding, Term						1 year				1 year
Class A Units [Member] | Series B Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right						1				1
Class of Warrant or Right, Exercise Price of Warrants or Rights						$ 1.55				$ 1.55
Warrants and Rights Outstanding, Term						5 years				5 years
Class B Units [Member] | Series A Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right						1				1
Class of Warrant or Right, Exercise Price of Warrants or Rights						$ 1.55				$ 1.55
Warrants and Rights Outstanding, Term						1 year				1 year
Class B Units [Member] | Series B Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right						1				1
Class of Warrant or Right, Exercise Price of Warrants or Rights						$ 1.55				$ 1.55
Warrants and Rights Outstanding, Term						5 years				5 years
November 2019 Offering [Member]
Proceeds from Issuance or Sale of Equity, Total						$ 11,500,000
Proceeds From Issuance of Common Stock, Net						$ 9,952,000
November 2019 Offering [Member] | Series A Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues						5,473,410
November 2019 Offering [Member] | Class A Units [Member]
Shares Issued, Price Per Share						$ 1.55				$ 1.55
Common Shares Per Unit						1				1
November 2019 Offering [Member] | Class B Units [Member]
Shares Issued, Price Per Share						$ 1.55				$ 1.55
Series A Convertible Preferred Stock Per Unit						1				1
November 2019 Offering [Member] | Class B Units [Member] | Series A Preferred Stock [Member]
Convertible Preferred Stock, Shares Issued upon Conversion						1				1
November 2019 Offering [Member] | Common Stock [Member]
Stock Issued During Period, Shares, New Issues						1,945,943				1,945,943	1,945,943
August 2019 ATM Facility [Member]
Proceeds From Issuance of Common Stock, Net											$ 6,322,000
Stock Issued During Period, Shares, New Issues											1,004,171
Aggregate Offering Price		$ 6,760,000					$ 6,760,000
August 2019 ATM Facility [Member] | Common Stock [Member]
Stock Issued During Period, Shares, New Issues											1,004,171
November 2017 ATM Facility [Member]
Proceeds From Issuance of Common Stock, Net						$ 1,193,000	$ 1,318,000					$ 1,193,000
Stock Issued During Period, Shares, New Issues						2,771	3,364				0	2,771
Aggregate Offering Price				$ 25,000,000			$ 25,000,000
November 2017 ATM Facility [Member] | Common Stock [Member]
Stock Issued During Period, Shares, New Issues												2,771
December 2018 Offering [Member]
Proceeds From Issuance of Common Stock, Net								$ 20,384,000
Stock Issued During Period, Shares, New Issues								147,285
Proceeds from Issuance of Common Stock								$ 22,093,000
December 2018 Offering [Member] | Common Stock [Member]
Stock Issued During Period, Shares, New Issues												147,285
February 2018 Offering [Member]
Proceeds From Issuance of Common Stock, Net			$ 32,214,000						$ 32,214,000
Stock Issued During Period, Shares, New Issues									115,000
Proceeds from Issuance of Common Stock			$ 34,500,000						$ 34,500,000
February 2018 Offering [Member] | Common Stock [Member]
Stock Issued During Period, Shares, New Issues												115,000