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Geographic And Customer Information (Comparison Of Geographic Revenues) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]      
Total revenues $ 1,165,095 $ 1,142,167 $ 1,059,366
U.S. [Member]      
Revenues from External Customers and Long-Lived Assets [Line Items]      
Total revenues 694,759 667,301 639,170
EMEA [Member]      
Revenues from External Customers and Long-Lived Assets [Line Items]      
Total revenues 211,349 207,474 193,623
Asia Pacific [Member]      
Revenues from External Customers and Long-Lived Assets [Line Items]      
Total revenues 106,526 127,298 83,456
Other [Member]      
Revenues from External Customers and Long-Lived Assets [Line Items]      
Total revenues $ 152,461 $ 140,094 $ 143,117