Note 1 - The Company and Basis of Presentation (Details Textual) - USD ($)							1 Months Ended						11 Months Ended	12 Months Ended
	Jan. 19, 2021	Jun. 09, 2020	Jun. 08, 2020	Apr. 20, 2020	Apr. 16, 2020	Nov. 12, 2019	Sep. 30, 2020	Aug. 31, 2020	Jun. 30, 2020	May 31, 2020	Feb. 29, 2020	Nov. 30, 2019	Nov. 30, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 31, 2021	Jan. 18, 2021	Dec. 16, 2020	Apr. 15, 2020
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)																2,473,785
Preferred Stock, Shares Authorized (in shares)															10,000,000	10,000,000
Proceeds from Warrant Exercises															$ 8,407,000
Payments of Warrant Issuance Costs				$ 334,000											334,000
Debt Conversion, Converted Instrument, Amount																35,529,000
Retained Earnings (Accumulated Deficit), Ending Balance															(219,826,000)	(197,911,000)
Cash and Cash Equivalents, at Carrying Value, Ending Balance															6,523,000	13,308,000
Working Capital															8,628,000
Net Cash Provided by (Used in) Operating Activities, Total															(15,234,000)	(31,236,000)
Net Cash Provided by (Used in) Financing Activities, Total															$ 9,230,000	$ 16,108,000
Series B Convertible Preferred Stock Into Common Stock [Member] | Minimum [Member]
Conversion of Stock, Conversion Rate (in dollars per share)						$ 15.30
Series B Convertible Preferred Stock Into Common Stock [Member] | Maximum [Member]
Conversion of Stock, Conversion Rate (in dollars per share)						$ 18.36
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 (in shares)						31,300
Series A and Series B Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)																$ 15.50				$ 6.10
Proceeds from Warrant Exercises					$ 3,089,000
Series A Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)												1	1
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)												$ 15.50	$ 15.50			$ 18.36
Warrants and Rights Outstanding, Term (Year)												1 year	1 year
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)												741,939	741,939			989,379
Stock Issued During Period, Shares, Warrant Exercises (in shares)					482,059			111,704	2,761	410	102,626
Proceeds from Warrant Exercises								$ 681,000	$ 17,000	$ 2,000	$ 1,591,000
Class of Warrant or Right, Outstanding (in shares)															0
Series B Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)												1	1
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)												$ 15.50	$ 15.50			$ 15.50
Warrants and Rights Outstanding, Term (Year)												5 years	5 years
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)												741,939	741,939		325,632	741,940
Stock Issued During Period, Shares, Warrant Exercises (in shares)					24,279		1,500	380,913	5,070		4,548
Proceeds from Warrant Exercises							$ 9,000	$ 2,324,000	$ 31,000		$ 70,000
Class of Warrant or Right, Outstanding (in shares)															325,632
Series A-2 Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)				482,059											392,830
Stock Issued During Period, Shares, Warrant Exercises (in shares)								89,230							392,830
Proceeds from Warrant Exercises								$ 568,000
Series B-2 Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)				24,279											20,380
Stock Issued During Period, Shares, Warrant Exercises (in shares)								3,899							20,380
Proceeds from Warrant Exercises								$ 25,000
Series A-2 and Series B-2 Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)				$ 6.371
Warrants and Rights Outstanding, Term (Year)				5 years
Class of Warrant or Right, Outstanding (in shares)				1,838,000
Warrants Issued Upon Conversion of Term Loan with CRG [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)																$ 15.50
Warrants and Rights Outstanding, Term (Year)						5 years
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)						989,379										741,940
Class of Warrants and Rights Outstanding, Exercise Price Percentage of Conversion Rate						120.00%
Class A Units [Member] | Series A Warrants [Member]
Warrants Per Unit (in shares)												1	1
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)												1	1
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)												$ 15.50	$ 15.50
Warrants and Rights Outstanding, Term (Year)												1 year	1 year
Class A Units [Member] | Series B Warrants [Member]
Warrants Per Unit (in shares)												1	1
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)												1	1
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)												$ 15.50	$ 15.50
Warrants and Rights Outstanding, Term (Year)												5 years	5 years
Class B Units [Member] | Series A Warrants [Member]
Warrants Per Unit (in shares)												1	1
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)												1	1
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)												$ 15.50	$ 15.50
Warrants and Rights Outstanding, Term (Year)												1 year	1 year
Class B Units [Member] | Series B Warrants [Member]
Warrants Per Unit (in shares)												1	1
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)												1	1
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)												$ 15.50	$ 15.50
Warrants and Rights Outstanding, Term (Year)												5 years	5 years
Common Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)															52,500
Common Stock [Member] | Series A and Series B Warrants [Member]
Stock Issued During Period, Shares, Warrant Exercises (in shares)															1,115,863
Common Stock [Member] | Series A-2 and Series B-2 Warrants [Member]
Stock Issued During Period, Shares, Warrant Exercises (in shares)															93,129
Series A Preferred Stock [Member]
Convertible Preferred Stock, Shares Issued upon Conversion (in shares)												1	1		1	1
Stock Issued During Period, Shares, New Issues (in shares)												547,345
Preferred Stock, Shares Outstanding, Ending Balance (in shares)															0	185,218			0
Preferred Stock, Shares Authorized (in shares)															547,345				547,345
Preferred Stock, Par or Stated Value Per Share (in dollars per share)															$ 0.0001	$ 0.0001			$ 0.0001
Subsequent Event [Member] | Series A and Series B Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)	$ 3.40																	$ 6.10
Subsequent Event [Member] | Series A-2 and Series B-2 Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)	1
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)	$ 3.40																	$ 6.371
Subsequent Event [Member] | Class A Units [Member] | Warrants Issued in Connection with Class A Units [Member]
Warrants Per Unit (in shares)	1
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)	1
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)	$ 3.40
Warrants and Rights Outstanding, Term (Year)	5 years
Subsequent Event [Member] | Class B Units [Member] | Warrants Issued in Connection with Class B Units [Member]
Warrants Per Unit (in shares)	1
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)	1
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)	$ 3.40
Warrants and Rights Outstanding, Term (Year)	5 years
Subsequent Event [Member] | Series C Preferred Stock [Member]
Preferred Stock, Shares Outstanding, Ending Balance (in shares)																	0
January 2021 Offering [Member] | Subsequent Event [Member]
Proceeds from Issuance or Sale of Equity, Total	$ 27,600,000
Shares Issued, Price Per Share (in dollars per share)	$ 3.40
Proceeds from Issuance or Sale of Equity, Net of Issuance Costs	$ 25,223,000
January 2021 Offering [Member] | Subsequent Event [Member] | Class A Units [Member]
Units Issued, Shares (in shares)	4,607,940
Shares Issued, Price Per Share (in dollars per share)	$ 3.40
Common Shares Per Unit (in shares)	1
January 2021 Offering [Member] | Subsequent Event [Member] | Class B Units [Member]
Units Issued, Shares (in shares)	2,450,880
Shares Issued, Price Per Share (in dollars per share)	$ 3.40
Series C Convertible Preferred Stock Per Unit (in shares)	1
January 2021 Offering [Member] | Subsequent Event [Member] | Series C Preferred Stock [Member]
Convertible Preferred Stock, Shares Issued upon Conversion (in shares)	1
Stock Issued During Period, Shares, New Issues (in shares)	2,450,880
Over-Allotment Option [Member] | Subsequent Event [Member]
Stock Issued During Period, Shares, New Issues (in shares)	1,058,820
Over-Allotment Option [Member] | Subsequent Event [Member] | Warrants Issued in Connection with January 2021 Offering [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)	1,058,820
Purchase Agreement with LPC [Member]
Shares Issued, Price Per Share (in dollars per share)		$ 6.50
Stock Issued During Period, Shares, New Issues (in shares)		52,500
Maximum Amount of Shares Issuable			$ 10,000,000
Stock Purchase Agreement Duration Period (Month)			2 years 180 days
Maximum Number of Shares Issuable on Any Business Day Selected by The Company (in shares)		25,000
Maximum Number of Shares Issuable on Any Business Day Selected by The Company in Certain Circumstances (in shares)		50,000
Purchase Agreement with LPC [Member] | Forecast [Member]
Proceeds from Issuance or Sale of Equity, Total														$ 9,700,000
November 2019 Offering [Member]
Proceeds from Issuance or Sale of Equity, Total												$ 11,500,000
Shares Issued, Price Per Share (in dollars per share)												$ 15.50	$ 15.50
Common Shares Per Unit (in shares)												1	1
Proceeds From Issuance of Common Stock, Net												$ 9,922,000
November 2019 Offering [Member] | Class A Units [Member]
Shares Issued, Price Per Share (in dollars per share)												$ 15.50	$ 15.50
Common Shares Per Unit (in shares)												1	1
November 2019 Offering [Member] | Class B Units [Member]
Shares Issued, Price Per Share (in dollars per share)												$ 15.50	$ 15.50
Series A Convertible Preferred Stock Per Unit (in shares)												1	1
November 2019 Offering [Member] | Common Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)												194,595	194,595			194,595
November 2019 Offering [Member] | Series A Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)												547,345	547,341
November 2019 Offering [Member] | Series A Preferred Stock [Member] | Class B Units [Member]
Convertible Preferred Stock, Shares Issued upon Conversion (in shares)												1	1