Note 7 - Stockholders' Equity (Details Textual) - USD ($)			3 Months Ended		6 Months Ended
	Mar. 27, 2020	Dec. 13, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	May 19, 2020
Proceeds from Issuance of Common Stock, Net					$ 5,214,000	$ 756,000
Share-based Payment Arrangement, Expense			$ 314,000	$ 125,000	$ 381,000	$ 206,000
Registered Direct Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)	1,000,002
Shares Issued, Price Per Share (in dollars per share)	$ 3.50
Proceeds from Issuance of Common Stock	$ 3,500,000
Payments of Stock Issuance Costs	$ 393,000
At The Market Offering Agreement [Member]
Stock Issued During Period, Shares, New Issues (in shares)					395,165
Proceeds from Issuance of Common Stock					$ 2,406,000
Payments of Stock Issuance Costs					$ 299,000
Maximum Offering Price for Issuance of Common Stock		$ 4,400,000					$ 15,280,313
Commission as Percentage of Gross Proceeds		3.00%
Shares Issued, Average Price Per Share (in dollars per share)					$ 5.77
Proceeds from Issuance of Common Stock, Net					$ 2,107,000