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Cash Equivalents And Restricted Cash And Securities (Summary Of Cash Equivalents And Restricted Securities) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Cash and Cash Equivalents [Line Items]        
Cash Equivalents, Cost Basis $ 42,236 $ 40,753 $ 57,341 $ 43,418
Restricted Securities, Cost Basis 747 776    
Cash [Member]        
Cash and Cash Equivalents [Line Items]        
Cost Basis   776    
Unrealized Holding Gains      
Restricted Securities, Estimated Market Value   776    
Money Market Funds [Member]        
Cash and Cash Equivalents [Line Items]        
Cash Equivalents, Cost Basis 1,445 372    
Restricted Securities, Cost Basis 747      
Unrealized Holding Gains    
Cash Equivalents, Estimated Market Value 1,445 $ 372    
Restricted Securities, Estimated Market Value $ 747