Note 7 - Note Payable (Details Textual) - USD ($)				12 Months Ended
	Nov. 12, 2019	Dec. 29, 2017	May 22, 2017	Dec. 31, 2021	Dec. 31, 2020
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)				2	2
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)				$ 2,720.00	$ 2,720.00
Notes Payable, Noncurrent, Total				$ 5,124,000	$ 4,518,000	[1]
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
May 2017 Issuance Related to 2017 Loan Agreement [Member]
Warrants and Rights Outstanding, Term (Year)			10 years
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)			223
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)			$ 9,500.00
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 and Rights Outstanding, Exercise Price Percentage of Conversion Rate	120.00%
The 2017 Loan Agreement [Member]
Notes Payable, Noncurrent, Total				5,124,000
The 2017 Loan Agreement [Member] | CRG LP [Member]
Debt Instrument, Face Amount			$ 20,000,000
Debt Agreement, Covenant, Additional Funding			10,000,000
Debt Agreement, Maximum Borrowing Capacity			$ 30,000,000
Proceeds from Lines of Credit, Total		$ 10,000,000
Debt Instrument, Term (Year)			6 years
Debt instrument, Interest Only Payment, Period (Year)			4 years
Debt Instrument, Interest Rate, Stated Percentage			12.50%
Debt Instrument, Interest Rate, Stated Percentage Deferred During Interest-only Period			4.00%
Debt Instrument, Prepayment Fee, Percentage			5.00%
Debt Instrument, Back-end Facility Fee Percentage of Principal	25.00%		5.00%
Paid-in-Kind Interest				602,000	532,000
Notes Payable, Noncurrent, Total				$ 5,124,000	$ 4,518,000

[1] The condensed consolidated balance sheet as of December 31, 2020 has been derived from the audited consolidated financial statements as of that date.