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Note 10 - Income Taxes (Details Textual) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount $ 530,000 $ 592,000
Liability for Uncertainty in Income Taxes, Current $ 0 $ 0
Open Tax Year 2016 2017 2018 2019 2020  
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member]    
Operating Loss Carryforwards, Subject to Expiration $ 57,500,000  
Operating Loss Carryforwards, Not Subject to Expiration $ 7,600,000