Note 12 - Common Stock (Details Textual)					1 Months Ended										3 Months Ended	11 Months Ended	12 Months Ended
	Jun. 09, 2020 USD ($) $ / shares shares	Jun. 08, 2020 USD ($)	Apr. 20, 2020 USD ($) $ / shares shares	Apr. 16, 2020 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 ($) shares	Dec. 31, 2019 USD ($) $ / shares shares	Nov. 30, 2019 USD ($) $ / shares shares	Oct. 31, 2019 USD ($) shares	Aug. 31, 2019 USD ($)	Mar. 31, 2019 USD ($) shares	Nov. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 16, 2020 shares	Apr. 15, 2020 $ / shares	Nov. 12, 2019 USD ($) $ / shares shares	May 22, 2017 USD ($) $ / shares shares
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)											2,473,785							2,473,785
Stock Issued During Period, Share, Restricted Common Shares (in shares)					4,709		3,453		2,832		3,068		774		28
Stock Issued During Period, Value, Restricted Common Shares | $					$ 25,000		$ 25,000		$ 24,000		$ 25,000		$ 25,000		$ 25,000		$ 74,000	$ 75,000
Warrants and Rights Outstanding | $											$ 3,502,000							3,502,000
Proceeds from Warrant Exercises | $																	8,407,000
Fair Value Adjustment of Warrants | $																	1,838,000
Payments of Warrant Issuance Costs | $			$ 334,000														334,000
Amortization of Debt Discount (Premium) | $																	3,000	$ 352,000
Debt Instrument, Unamortized Discount, Total | $																	$ 9,000
Class of Warrants or Rights, Exercises in Period (in shares)																	1,209,000	0
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)																	42,404	140
The 2017 Loan Agreement [Member]
Debt Issuance Costs, Net, Total | $																	$ 790,000
Debt Instrument, Unamortized Discount, Total | $																	$ 9,000
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 A Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)												547,345
Convertible Preferred Stock, Shares Issued upon Conversion (in shares)											1	1				1	1	1
Preferred Stock, Shares Outstanding, Ending Balance (in shares)											185,218						0	185,218	0
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) | $ / shares											$ 18.36	$ 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)											989,379	741,939				741,939		989,379
Warrants and Rights Outstanding | $												$ 1,210,000				$ 1,210,000
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 A Warrants [Member] | Measurement Input, Expected Dividend Rate [Member]
Warrants and Rights Outstanding, Measurement Input												0				0
Series A Warrants [Member] | Measurement Input, Price Volatility [Member]
Warrants and Rights Outstanding, Measurement Input												91.1				91.1
Series A Warrants [Member] | Measurement Input, Risk Free Interest Rate [Member]
Warrants and Rights Outstanding, Measurement Input												1.59				1.59
Series A Warrants [Member] | Measurement Input, Expected Term [Member]
Warrants and Rights Outstanding, Measurement Input												1				1
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) | $ / shares											$ 15.50	$ 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)											741,940	741,939				741,939	325,632	741,940
Warrants and Rights Outstanding | $												$ 2,871,000				$ 2,871,000
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 B Warrants [Member] | Measurement Input, Expected Dividend Rate [Member]
Warrants and Rights Outstanding, Measurement Input												0				0
Series B Warrants [Member] | Measurement Input, Price Volatility [Member]
Warrants and Rights Outstanding, Measurement Input												0.688				0.688
Series B Warrants [Member] | Measurement Input, Risk Free Interest Rate [Member]
Warrants and Rights Outstanding, Measurement Input												0.0158				0.0158
Series B Warrants [Member] | Measurement Input, Expected Term [Member]
Warrants and Rights Outstanding, Measurement Input												5				5
Series A and Series B Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares											$ 15.50							$ 15.50		$ 6.10
Warrants and Rights Outstanding | $												$ 4,081,000				$ 4,081,000
Proceeds from Warrant Exercises | $				$ 3,089,000
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			$ 6.371
Warrants and Rights Outstanding, Term (Year)			5 years
Class of Warrant or Right, Outstanding (in shares)			1,838,000
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			0.00841
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
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) | $ / shares											$ 15.50							$ 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)											741,940							741,940			989,379
Warrants and Rights Outstanding | $																					$ 3,502,000
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 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																					0.688
Warrants Issued Upon Conversion of Term Loan with CRG [Member] | Measurement Input, Risk Free Interest Rate [Member]
Warrants and Rights Outstanding, Measurement Input																					0.0158
Warrants Issued Upon Conversion of Term Loan with CRG [Member] | Measurement Input, Expected Term [Member]
Warrants and Rights Outstanding, Measurement Input																					5
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							$ 9,500				$ 9,500
Warrants and Rights Outstanding, Term (Year)																						10 years
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)											223							223				223
Warrants and Rights Outstanding | $																						$ 940,000
May 2017 Issuance Related to 2017 Loan Agreement [Member] | Measurement Input, Expected Dividend Rate [Member]
Warrants and Rights Outstanding, Measurement Input																						0
May 2017 Issuance Related to 2017 Loan Agreement [Member] | Measurement Input, Price Volatility [Member]
Warrants and Rights Outstanding, Measurement Input																						55.1
May 2017 Issuance Related to 2017 Loan Agreement [Member] | Measurement Input, Risk Free Interest Rate [Member]
Warrants and Rights Outstanding, Measurement Input																						2.25
May 2017 Issuance Related to 2017 Loan Agreement [Member] | Measurement Input, Expected Term [Member]
Warrants and Rights Outstanding, Measurement Input																						10
Class A Units [Member] | 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) | $ / shares												$ 15.50				$ 15.50
Warrants and Rights Outstanding, Term (Year)												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 (in shares)												1				1
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares												$ 15.50				$ 15.50
Warrants and Rights Outstanding, Term (Year)												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 (in shares)												1				1
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares												$ 15.50				$ 15.50
Warrants and Rights Outstanding, Term (Year)												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 (in shares)												1				1
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | $ / shares												$ 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
Stock Issued During Period, Share, Restricted Common Shares (in shares)																	10,995	3,869
Stock Issued During Period, Value, Restricted Common Shares | $
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
Purchase Agreement with LPC [Member]
Maximum Amount of Shares Issuable | $		$ 10,000,000
Stock Purchase Agreement Duration Period (Month)		2 years 180 days
Stock Issued During Period, Shares, New Issues (in shares)	52,500
Shares Issued, Price Per Share (in dollars per share) | $ / shares	$ 6.50
Maximum Number of Shares Issuable on Any Business Day Selected by The Company (in shares)	25,000
Maximum Number of Shares Issuable on Regular Purchase, Closing Sale Price Not Below $10.00 (in shares)	30,000
Maximum Number of Shares Issuable on Regular Purchase, Closing Sale Price Not Below $20.00 (in shares)	50,000
Maximum Number of Shares Issuable Any single Regular Purchase (in shares)	1,000,000
Payments of Stock Issuance Costs | $	$ 494,000																$ 494,000
Purchase Agreement with LPC [Member] | Commitment Fee [Member]
Payments of Stock Issuance Costs | $	$ 325,000
November 2019 Offering [Member]
Shares Issued, Price Per Share (in dollars per share) | $ / shares												$ 15.50				$ 15.50
Payments of Stock Issuance Costs | $																	$ 33,000
Proceeds from Issuance or Sale of Equity, Total | $												$ 11,500,000
Proceeds From Issuance of Common Stock, Net | $												$ 9,922,000
Common Shares Per Unit (in shares)												1				1
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] | Class A Units [Member]
Shares Issued, Price Per Share (in dollars per share) | $ / shares												$ 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) | $ / shares												$ 15.50				$ 15.50
Series A Convertible Preferred Stock Per Unit (in shares)												1				1
November 2019 Offering [Member] | Class B Units [Member] | Series A Preferred Stock [Member]
Convertible Preferred Stock, Shares Issued upon Conversion (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
August 2019 ATM Facility [Member]
Stock Issued During Period, Shares, New Issues (in shares)																		100,423
Proceeds From Issuance of Common Stock, Net | $																		$ 6,322,000
Aggregate Offering Price | $														$ 6,760,000
Common Stock, Shares, Remaining Shares to be Issued (in shares)											0							0
August 2019 ATM Facility [Member] | Common Stock [Member]
Stock Issued During Period, Shares, New Issues (in shares)																		100,418
November 2017 ATM Facility [Member]
Stock Issued During Period, Shares, New Issues (in shares)																		0
Aggregate Offering Price | $														$ 25,000,000