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Long-Term Debt (Schedule Of Long-term Debt) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Line of Credit Facility [Line Items]    
Notes payable to a bank, with interest only payment until maturity   $ 2,400
Installment notes bearing interest at the rate of 4.16% to 4.6% per annum collateralized by vehicles with monthly payments including interest, insurance and maintenance of approximately $10 $ 90 $ 102
Periodic payments including interest, insurance and maintenance $ 10  
Maximum [Member]    
Line of Credit Facility [Line Items]    
Interest rate per annum 4.60%  
Minimum [Member]    
Line of Credit Facility [Line Items]    
Interest rate per annum 4.16%