Note 10 - Preferred Stock and Common Stock Warrants - Allocation of Net Cash Proceeds (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Proceeds from equity issuance	$ 0	$ 70,945
Series B Warrants [Member]
Net proceeds - Initial Fair Value Allocation		1,936
Per balance sheet upon issuance		1,936
Convertible Preferred Stock [Member]
Proceeds from equity issuance		20,945
Equity issuance costs		0
Net proceeds - Initial Fair Value Allocation		20,945
Series B Convertible Preferred Stock [Member]
Net proceeds - Initial Fair Value Allocation		19,009
Per balance sheet upon issuance		$ 19,009