Note 1 - The Company and Basis of Presentation (Details Textual) - USD ($)					1 Months Ended	2 Months Ended	3 Months Ended
	Jul. 02, 2021	Jan. 19, 2021	Jun. 09, 2020	Jun. 08, 2020	Feb. 28, 2021	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Mar. 14, 2022	Dec. 31, 2021	Jan. 31, 2021	Jan. 18, 2021	Nov. 26, 2019
Fair Value Adjustment of Warrants							$ (0)	$ 287,000
Proceeds from Warrant Exercises							$ 0	179,000
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)							9,793,599
Preferred Stock, Shares Authorized (in shares)							10,000,000			10,000,000
Retained Earnings (Accumulated Deficit), Total							$ (247,739,000)			$ (241,853,000)
Cash and Cash Equivalents, at Carrying Value, Total							14,045,000			$ 19,162,000
Working Capital							7,236,000
Net Cash Provided by (Used in) Operating Activities, Total							$ (5,087,000)	$ (3,253,000)
Series B Preferred Stock [Member]
Stock Issued During Period, Shares, Warrant Exercises (in shares)						40,000
Proceeds from Warrant Exercises						$ 136,000
Preferred Stock, Shares Outstanding, Ending Balance (in shares)						36,937	41,767	36,937		40,504
Convertible Preferred Stock, Shares Issued upon Conversion (in shares)						2,414,283	2,729,869	2,414,283		2,647,320			2,729,869
January 2021 Offering Warrants [Member]
Stock Issued During Period, Shares, Warrant Exercises (in shares)						12,760
Proceeds from Warrant Exercises						$ 43,000
Series B Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)							285,632
Series A-2 Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)							392,830
Series B-2 Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)							20,380
Series C Preferred Stock [Member]
Preferred Stock, Shares Outstanding, Ending Balance (in shares)							0		0	0	0
Convertible Preferred Stock, Shares Issued upon Conversion (in shares)							1
Preferred Stock, Shares Authorized (in shares)									2,450,880
Series A and Series B Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)		$ 3.40
Fair Value Adjustment of Warrants		$ 287,000
Series B Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)		$ 3.40										$ 6.10
Stock Issued During Period, Shares, Warrant Exercises (in shares)					40,000
Proceeds from Warrant Exercises					$ 136,000
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)							285,632
Series A-2 and Series B-2 Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)		$ 3.40										$ 6.371
Fair Value Adjustment of Warrants		$ 287,000
Warrants Issued in Connection with Class A Units [Member] | Class A Units [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)		$ 3.40
Warrants Per Unit (in shares)		1
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)		1
Warrants and Rights Outstanding, Term (Year)		5 years
Warrants Issued in Connection with Class B Units [Member] | Class B Units [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)		$ 3.40
Warrants Per Unit (in shares)		1
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)		1
Warrants and Rights Outstanding, Term (Year)		5 years
Warrants Issued in Connection with January 2021 Offering [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)											$ 3.40
Stock Issued During Period, Shares, Warrant Exercises (in shares)						12,760
Proceeds from Warrant Exercises						$ 43,000
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)		8,117,640					8,104,880				8,117,640
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)											1
Warrants and Rights Outstanding, Term (Year)											5 years
Universal Shelf Registration Statement [Member]
Universal Shelf Registration Statement, Proposed Maximum Securities Offering	$ 75,000,000
Universal Shelf Registration Statement, Maximum Capacity							$ 75,000,000
Stock Issued During Period, Shares, New Issues (in shares)							0
Proceeds from Issuance or Sale of Equity, Total							$ 0
January 2021 Offering [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		$ 25,122,000
January 2021 Offering [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
Warrants Per Unit (in shares)		1
January 2021 Offering [Member] | Class B Units [Member]
Units Issued, Shares (in shares)		2,450,880
Shares Issued, Price Per Share (in dollars per share)		$ 3.40
Warrants Per Unit (in shares)		1
Series C Convertible Preferred Stock Per Unit (in shares)		1
January 2021 Offering [Member] | Series C Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)		2,450,880
Convertible Preferred Stock, Shares Issued upon Conversion (in shares)						1		1
Over-Allotment Option [Member]
Stock Issued During Period, Shares, New Issues (in shares)		1,058,820
Over-Allotment Option [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]
Stock Issued During Period, Shares, New Issues (in shares)			52,500
Shares Issued, Price Per Share (in dollars per share)			$ 6.50
Maximum Amount of Shares Issuable				$ 10,000,000
Stock Purchase Agreement Duration Period (Month)				30 months
Equity Facility, Remaining Financing Commitment							$ 9,000,000