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Cash Equivalents And Restricted Securities (Summary Of Cash Equivalents And Restricted Securities) (Details) - USD ($)
$ in Thousands
6 Months Ended 12 Months Ended
Jun. 30, 2017
Dec. 31, 2016
Jun. 30, 2016
Dec. 31, 2015
Cash and Cash Equivalents [Line Items]        
Cash Equivalents, Cost Basis $ 52,507 $ 56,642 $ 46,935 $ 37,588
Restricted Securities, Cost Basis 741 699    
Money Market Funds [Member]        
Cash and Cash Equivalents [Line Items]        
Cash Equivalents, Cost Basis 370 3,466    
Restricted Securities, Cost Basis 741 699    
Unrealized Holding Gains    
Cash Equivalents, Estimated Market Value 370 3,466    
Restricted Securities, Estimated Market Value $ 741 $ 699