Note 7 - Stockholders' Equity (Details Textual) - USD ($)		6 Months Ended
	Jan. 13, 2022	Jun. 30, 2022	Jun. 30, 2021	Mar. 31, 2022	Feb. 03, 2022
Proceeds from Issuance of Common Stock, Net		$ 2,044,000	$ 6,832,000
The 2016 Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares)	392,500
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized (in shares)	1,200,000
At The Market Offering Agreement [Member]
Maximum Offering Price for Issuance of Common Stock				$ 18,573,000
Additional Common Stock, Shares Authorized					$ 4,275,000
Stock Issued During Period, Shares, New Issues (in shares)		5,315,422
Proceeds from Issuance of Common Stock		$ 2,255,000
Shares Issued, Average Price Per Share (in dollars per share)		$ 0.42
Proceeds from Issuance of Common Stock, Net		$ 2,044,000
Payments of Stock Issuance Costs		$ 211,000
At The Market Offering Agreement [Member] | Minimum [Member]
Maximum Offering Price for Issuance of Common Stock					15,280,000
At The Market Offering Agreement [Member] | Maximum [Member]
Maximum Offering Price for Issuance of Common Stock					$ 19,555,000