Note 11 - Stockholders' Equity (Details Textual) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands					12 Months Ended
	Nov. 19, 2021	Jun. 01, 2020	Nov. 21, 2019	Nov. 18, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Nov. 17, 2021	Apr. 24, 2020
Stock Issued During Period, Shares, New Issues (in shares)		22,044		43,621	3,846	22,044	43,621
Shares Issued, Price Per Share (in dollars per share)		$ 4.50	$ 1.69	$ 1.45
Proceeds from Issuance of Common Stock				$ 58,500	$ 50,000	$ 93,279	$ 58,500
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)			11,765
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)			$ 0.01
Proceeds from Issuance of Warrants			$ 19,882			$ 14,817	$ 19,882
Maximum Aggregate Offering Price									$ 500,000
Proceeds from Issuance or Sale of Equity, Total		$ 108,096,000
Common Stock Purchase Agreement with RPI [Member]
Stock Issued During Period, Shares, New Issues (in shares)	3,846,154
Shares Issued, Price Per Share (in dollars per share)	$ 13.00							$ 13.00
Proceeds from Issuance of Common Stock	$ 50,000
Shares Issued, Price Per Share, Premium (in dollars per share)								1.11
Shares Issued, Price Per Share, Closing Price (in dollars per share)								$ 11.89
Shares Issued, Common Stock, Premium								$ 4,269
Warrants Issued in Public Offering [Member]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)		3,511
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)		$ 0.01
Class of Warrant or Right, Warrants Issued, Price Per Warrant (in dollars per share)		$ 4.49