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Summary Of Significant Accounting Policies (Allowance For Doubtful Accounts) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]      
Allowance as of the beginning of the year $ 5,026 $ 4,530 $ 4,888
Additions expensed during the year 5,317 6,053 5,802
Net deductions (5,211) (5,557) (6,160)
Allowance as of the end of the year $ 5,132 $ 5,026 $ 4,530