Note 7 - Income Taxes (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ 5,334,000	$ 4,148,000
Unrecognized Tax Benefits, Ending Balance	1,200,000
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0
Deferred Tax Assets, Net, Total	0
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member]
Operating Loss Carryforwards, Total	$ 325,000,000
Open Tax Year	2017 2018 2019 2020
Open Tax Period (Year)	3 years
State and Local Jurisdiction [Member] | California Franchise Tax Board [Member]
Operating Loss Carryforwards, Total	$ 237,000,000
Open Tax Year	2016 2017 2018 2019 2020
Open Tax Period (Year)	4 years