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Investments In Securities (Schedule of Equity Securities) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Sep. 30, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity Securities, Cost $ 26,003 $ 27,382
Gross Unrealized Gains 21,376  
Gross Unrealized Losses 12  
Equity Securities, Estimated Fair Value 47,367 51,372
Common Stock    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity Securities, Cost 26,003 27,382
Gross Unrealized Gains 21,376  
Gross Unrealized Losses 12  
Equity Securities, Estimated Fair Value $ 47,367 $ 51,372