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Marketable Securities (Schedule Of Marketable Securities) (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 55,467 $ 58,937
Gross Unrealized Holding Gains 8,535 8,693
Gross Unrealized Holding Losses (81) (459)
Fair Value 63,921 67,171
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 1,198 1,198
Gross Unrealized Holding Gains 7,487 8,162
Gross Unrealized Holding Losses 0 0
Fair Value 8,685 9,360
Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 54,269 57,739
Gross Unrealized Holding Gains 1,048 531
Gross Unrealized Holding Losses (81) (459)
Fair Value $ 55,236 $ 57,811