Note 12 - Common Stock (Details Textual)									1 Months Ended								2 Months Ended	9 Months Ended	12 Months Ended
	May 04, 2021 USD ($) $ / shares shares	Mar. 31, 2021 USD ($) $ / shares shares	Jan. 19, 2021 USD ($) $ / shares shares	Jun. 09, 2020 USD ($) $ / shares shares	Jun. 08, 2020 USD ($) $ / shares shares	Apr. 20, 2020 USD ($) $ / shares shares	Apr. 16, 2020 USD ($) shares	Apr. 15, 2020 USD ($) $ / shares	Mar. 31, 2021 USD ($) $ / shares shares	Feb. 28, 2021 USD ($) shares	Sep. 30, 2020 USD ($) shares	Aug. 31, 2020 USD ($) shares	Jun. 30, 2020 USD ($) shares	May 31, 2020 USD ($) shares	Mar. 31, 2020 USD ($) shares	Feb. 29, 2020 USD ($) shares	Mar. 31, 2021 USD ($) $ / shares shares	Sep. 30, 2021 shares	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Jun. 23, 2021	Jan. 31, 2021 $ / shares shares	Jan. 18, 2021 $ / shares	Dec. 31, 2019 $ / shares	Nov. 12, 2019 USD ($) $ / shares shares	May 22, 2017 $ / shares shares
Proceeds from Issuance of Common Stock | $																			$ 25,122,000	$ 0
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares																			$ 2,720.00	$ 2,720.00
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)																			2	2
Stock Issued During Period, Shares, Warrant Exercises (in shares)																			52,760	1,209,000
Proceeds from Warrant Exercises | $																			$ 179,000	$ 8,407,000
Stock Issued During Period, Share, Restricted Common Shares (in shares)											4,709		3,453		2,832				0
Stock Issued During Period, Value, Restricted Common Shares | $											$ 25,000		$ 25,000		$ 24,000					74,000
Amortization of Debt Discount (Premium) | $																			$ 4,000	3,000
Debt Instrument, Unamortized Discount, Total | $																			5,000
Fair Value Adjustment of Warrants | $																			373,000	1,838,000
Payments of Warrant Issuance Costs | $						$ 334,000													$ (0)	$ 334,000
Class of Warrant or Right Number of Securities Called by Warrants or Rights Cancelled In Period (in shares)																			0	0
Class Of Warrant Or Right, Number Of Securities Called By Warrants Or Rights Expired In Period (in shares)																			6	42,404
Series B Convertible Preferred Stock Into Common Stock [Member] | Minimum [Member]
Conversion of Stock, Conversion Rate (in dollars per share) | $ / shares																									$ 15.30
Series B Convertible Preferred Stock Into Common Stock [Member] | Maximum [Member]
Conversion of Stock, Conversion Rate (in dollars per share) | $ / shares																									$ 18.36
Series C Preferred Stock [Member]
Preferred Stock, Shares Outstanding, Ending Balance (in shares)		0							0								0		0	0		0
Warrants Issued in Connection with January 2021 Offering [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) | $ / shares																						$ 3.40
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)		8,104,880	8,117,640						8,104,880								8,104,880		8,104,880			8,117,640
Stock Issued During Period, Shares, Warrant Exercises (in shares)																	12,760
Proceeds from Warrant Exercises | $																	$ 43,000
May 2017 Issuance Related to 2017 Loan Agreement [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares																										$ 9,500.00
Warrants and Rights Outstanding, Term (Year)																										10 years
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)																										223
Warrants Issued Upon Conversion of Term Loan with CRG [Member]
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
Class of Warrants or Rights, Outstanding, Percentage of Common Stock																									15.00%
Class of Warrants and Rights Outstanding, Exercise Price Percentage of Conversion Rate																									120.00%
Warrants and Rights Outstanding | $																									$ 3,502,000
Warrants Issued Upon Conversion of Term Loan with CRG [Member] | Measurement Input, Expected Dividend Rate [Member]
Warrants and Rights Outstanding, Measurement Input																									0
Warrants Issued Upon Conversion of Term Loan with CRG [Member] | Measurement Input, Price Volatility [Member]
Warrants and Rights Outstanding, Measurement Input																									68.8
Warrants Issued Upon Conversion of Term Loan with CRG [Member] | Measurement Input, Risk Free Interest Rate [Member]
Warrants and Rights Outstanding, Measurement Input																									1.58
Warrants Issued Upon Conversion of Term Loan with CRG [Member] | Measurement Input, Expected Term [Member]
Warrants and Rights Outstanding, Measurement Input																									5
Series A Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)																			0
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
Series B Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares			$ 3.40																				$ 6.10
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)																			285,632
Stock Issued During Period, Shares, Warrant Exercises (in shares)							24,279			40,000	1,500	380,913	5,070			4,548
Proceeds from Warrant Exercises | $										$ 136,000	$ 9,000	$ 2,324,000	$ 31,000			$ 70,000
Series A and Series B Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares			$ 3.40					$ 6.10																$ 15.50
Proceeds from Warrant Exercises | $							$ 3,089,000
Fair Value Adjustment of Warrants | $			$ 287,000					$ 1,838,000
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) | $ / shares			$ 3.40			$ 6.371																	$ 6.371
Warrants and Rights Outstanding, Term (Year)						5 years
Fair Value Adjustment of Warrants | $			$ 287,000
Class of Warrant or Right, Outstanding (in shares)						1,838,000
Payments of Warrant Issuance Costs | $						$ 334,000
Series A-2 and Series B-2 Warrants [Member] | Measurement Input, Expected Dividend Rate [Member]
Warrants and Rights Outstanding, Measurement Input						0
Series A-2 and Series B-2 Warrants [Member] | Measurement Input, Price Volatility [Member]
Warrants and Rights Outstanding, Measurement Input						84.1
Series A-2 and Series B-2 Warrants [Member] | Measurement Input, Risk Free Interest Rate [Member]
Warrants and Rights Outstanding, Measurement Input						0.35
Series A-2 and Series B-2 Warrants [Member] | Measurement Input, Expected Term [Member]
Warrants and Rights Outstanding, Measurement Input						5
Series B, A-2 and B-2 Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares	$ 2.817
Fair Value Adjustment of Warrants | $	$ 86,000
January 2021 Offering Warrants [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)																			8,104,880
Stock Issued During Period, Shares, Warrant Exercises (in shares)									4,000	8,760
Proceeds from Warrant Exercises | $									$ 13,000	$ 30,000
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) | $ / shares			$ 3.40
Warrants and Rights Outstanding, Term (Year)			5 years
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) | $ / shares			$ 3.40
Warrants and Rights Outstanding, Term (Year)			5 years
Purchase Agreement with LPC [Member]
Maximum Amount of Shares Issuable | $					$ 10,000,000
Stock Purchase Agreement Duration Period (Month)					30 months
Stock Purchase Agreement, Maximum Issuable Shares (in shares)					301,762
Stock Purchase Agreement, Maximum Issuable Shares, Percent of Outstanding Stock					19.99%
Stock Purchase Agreement, Share Price Covenant Trigger (in dollars per share) | $ / shares					$ 6.46
Stock Issued During Period, Shares, New Issues (in shares)	250,000			52,500
Shares Issued, Price Per Share (in dollars per share) | $ / shares	$ 2.817			$ 6.50
Proceeds from Issuance of Common Stock | $	$ 704,000			$ 341,000
Payments of Stock Issuance Costs | $				494,000															$ 70,000	$ 494,000
Equity Facility, Remaining Financing Commitment | $																			$ 9,000,000
Purchase Agreement with LPC [Member] | Commitment Fee [Member]
Payments of Stock Issuance Costs | $				$ 325,000
First Amendment to the LPC Purchase Agreement [Member]
Stock Purchase Agreement, Maximum Issuable Shares (in shares)		2,068,342							2,068,342								2,068,342
Stock Purchase Agreement, Maximum Issuable Shares, Percent of Outstanding Stock		19.99%							19.99%								19.99%				20.00%
Stock Purchase Agreement, Share Price Covenant Trigger (in dollars per share) | $ / shares		$ 2.99							$ 2.99								$ 2.99
Stock Issued During Period, Shares, New Issues (in shares)	250,000
Shares Issued, Price Per Share (in dollars per share) | $ / shares	$ 2.817
Proceeds from Issuance of Common Stock | $	$ 704,000
Payments of Stock Issuance Costs | $		$ 70,000
January 2021 Offering [Member]
Shares Issued, Price Per Share (in dollars per share) | $ / shares			$ 3.40
Proceeds from Issuance or Sale of Equity, Total | $			$ 27,600,000
Proceeds from Issuance or Sale of Equity, Net of Issuance Costs | $			$ 25,122,000
January 2021 Offering [Member] | Series C Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)			2,450,880
January 2021 Offering [Member] | Class A Units [Member]
Shares Issued, Price Per Share (in dollars per share) | $ / shares			$ 3.40
Units Issued, Shares (in shares)			4,607,940
Common Shares Per Unit (in shares)			1
Warrants Per Unit (in shares)			1
January 2021 Offering [Member] | Class B Units [Member]
Shares Issued, Price Per Share (in dollars per share) | $ / shares			$ 3.40
Units Issued, Shares (in shares)			2,450,880
Common Shares Per Unit (in shares)			1
Warrants Per Unit (in shares)			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