Segment Reporting (Schedule Of Revenue By Principal Geographic Area) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 399,685	$ 406,387	$ 413,343	$ 382,477	$ 351,959	$ 383,523	$ 390,122	$ 360,203	$ 1,601,892	$ 1,485,807	$ 1,377,058
Americas [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									1,084,309	952,757	899,185
Americas [Member] | United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									980,281	848,928	802,345
Americas [Member] | Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									69,303	69,743	69,947
Americas [Member] | Latin America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									34,725	34,086	26,893
Europe, The Middle East And Africa [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									348,333	366,390	326,685
Europe, The Middle East And Africa [Member] | Germany [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									73,395	85,189	78,109
Europe, The Middle East And Africa [Member] | United Kingdom [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									74,879	74,131	65,027
Europe, The Middle East And Africa [Member] | France [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									46,972	53,322	49,093
Europe, The Middle East And Africa [Member] | Italy [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									25,903	28,794	26,443
Europe, The Middle East And Africa [Member] | Spain [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									19,998	21,566	20,194
Europe, The Middle East And Africa [Member] | Switzerland [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									15,631	14,544	12,246
Europe, The Middle East And Africa [Member] | Netherlands [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									11,645	10,643	9,352
Europe, The Middle East And Africa [Member] | Other Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									79,910	78,201	66,221
Asia Pacific Region [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									169,250	166,660	151,188
Asia Pacific Region [Member] | Australia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									49,274	58,448	53,063
Asia Pacific Region [Member] | Japan [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									43,171	44,132	44,869
Asia Pacific Region [Member] | China [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									40,619	34,674	29,044
Asia Pacific Region [Member] | Other Asia Pacific [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									$ 36,186	$ 29,406	$ 24,212