Consolidated Statements of Stockholders' Equity (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
February 2020 Stock Offering [Member]
Issued for cash - sale of common stock, issuance costs		$ 709
The 2019 ATM Agreement [Member]
Issued for cash - sale of common stock, issuance costs		471
The 2020 ATM Agreement [Member]
Issued for cash - sale of common stock, issuance costs		108
Lincoln Park Transaction [Member]
Issued for cash - sale of common stock, issuance costs		$ 575
Q1 2021 Stock Sale [Member]
Issued for cash - sale of common stock, issuance costs	$ 6,159
Equity Purchase Agreement [Member]
Issued for cash - sale of common stock, issuance costs	$ 403