Note 10 - Stockholders' Equity (Details Textual) - USD ($)	3 Months Ended		16 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	May 19, 2020	Dec. 13, 2019
Proceeds from Issuance of Common Stock, Net	$ 6,832,000	$ 3,220,000
Share-based Payment Arrangement, Expense	$ 258,000	$ 67,000
At The Market Offering Agreement [Member]
Maximum Offering Price for Issuance of Common Stock				$ 15,280,313	$ 4,400,000
Stock Issued During Period, Shares, New Issues (in shares)	2,976,832		5,597,484
Proceeds from Issuance of Common Stock			$ 15,280,000
Shares Issued, Price Per Share (in dollars per share)	$ 2.73		$ 2.73
Proceeds from Issuance of Common Stock, Net	$ 6,832,000		$ 14,568,000
Payments of Stock Issuance Costs	$ 224,000		$ 712,000