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Investments In Securities (Schedule of Equity Securities) (Details) - USD ($)
$ in Thousands
6 Months Ended 12 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cost $ 26,956 $ 26,003
Estimated Fair Value 48,026 47,367
Common Stock    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cost 26,956 26,003
Gross Unrealized Gains 21,283 21,376
Gross Unrealized Losses 213 12
Estimated Fair Value $ 48,026 $ 47,367