Note 2 - Summary of Significant Accounting Policies (Details Textual) $ in Thousands	6 Months Ended
	Jun. 30, 2023 USD ($) shares	Mar. 31, 2023 shares	Dec. 31, 2022 USD ($) shares
Retained Earnings (Accumulated Deficit)	$ (648,075)		$ (616,127)
Working Capital (Deficit)	7,800
Cash and Cash Equivalents, at Carrying Value	$ 18,359		$ 53,689
Number of Operating Segments	1
Common Stock, Shares Authorized (in shares) | shares	250,000,000	250,000,000	100,000,000
Minimum [Member]
Property, Plant and Equipment, Useful Life (Year)	3 years
Maximum [Member]
Property, Plant and Equipment, Useful Life (Year)	5 years