Segment Information (Revenues By Geographic Location) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	$ 777,857	$ 690,925	$ 693,227	$ 662,677	$ 734,584	$ 668,736	$ 673,987	$ 658,773	$ 2,824,686	$ 2,736,080	$ 2,646,154
Americas
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues									1,644,008	1,598,896	1,487,364
EMEA
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues									888,072	863,517	873,620
APJ
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues									$ 292,606	$ 273,667	$ 285,170