Note 8 - Stockholders' Equity (Details Textual) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended
	Mar. 25, 2021	Sep. 17, 2020	Mar. 31, 2021	Mar. 31, 2020
Stock and Warrants Issued, Price Per Share (in dollars per share)	$ 3.25
Proceeds from Issuance or Sale of Equity, Total	$ 27,400
Stock Issued During Period, Shares, New Issues (in shares)	9,230,500
Proceeds from Issuance of Common Stock			$ 570
March 2021 Warrants [Member]
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)	$ 3.60
Warrants and Rights Outstanding, Term (Year)	5 years
March 2021 Public Offering [Member]
Equity Issued During Period, Units, New Issues (in shares)	9,230,500
Units, Number of Securities Called by Each Unit (in shares)	1
Stock and Warrants Issued, Price Per Share (in dollars per share)	$ 3.25
Proceeds from Issuance or Sale of Equity, Gross Amount	$ 30,000
Proceeds from Issuance or Sale of Equity, Total	$ 27,400
Units, Number of Warrants Called by Each Unit (in shares)	1
September 2020 At The Market Offering [Member]
Proceeds from Issuance or Sale of Equity, Total			$ 600
Shares Authorized to Be Offered and Sold Under Offering Agreement, Value		$ 10,000
Stock Issued During Period, Shares, New Issues (in shares)			105,083
Proceeds from Issuance of Common Stock			$ 600
September 2020 At The Market Offering [Member] | Ladenburg [Member]
Commission Fee, Percent Fee		3.00%