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Note 1 - Summary of Significant Accounting Policies (Details Textual) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Impairment of Deferred Development Costs   $ 0 $ 0
Asset Impairment Charges   0 0
Operating Leases, Income Statement, Lease Revenue   5,527,000 $ 5,324,000
Operating Leases, Rent Expense, Net   50,000  
Operating Leases, Future Minimum Payments Due   34,000  
Revenue from Contract with Customer, Excluding Assessed Tax   $ 18,900,000  
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent   35.00% 35.00%
Scenario, Forecast [Member]      
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent 21.00%    
Minimum [Member]      
Property, Plant and Equipment, Useful Life   3 years  
Maximum [Member]      
Property, Plant and Equipment, Useful Life   40 years