Segment Reporting (Schedule Of Revenue By Principal Geographic Area) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 442,996	$ 448,308	$ 466,569	$ 417,550	$ 399,685	$ 406,387	$ 413,343	$ 382,477	$ 1,775,423	$ 1,601,892	$ 1,485,807
Americas [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									1,203,390	1,084,309	952,757
Americas [Member] | United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									1,089,595	980,281	848,928
Americas [Member] | Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									74,923	69,303	69,743
Americas [Member] | Latin America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									38,872	34,725	34,086
Europe, The Middle East And Africa [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									375,763	348,333	366,390
Europe, The Middle East And Africa [Member] | Germany [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									80,156	73,395	85,189
Europe, The Middle East And Africa [Member] | United Kingdom [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									77,671	74,879	74,131
Europe, The Middle East And Africa [Member] | France [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									51,204	46,972	53,322
Europe, The Middle East And Africa [Member] | Italy [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									28,907	25,903	28,794
Europe, The Middle East And Africa [Member] | Spain [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									24,268	19,998	21,566
Europe, The Middle East And Africa [Member] | Switzerland [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									16,361	15,631	14,544
Europe, The Middle East And Africa [Member] | Netherlands [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									14,049	11,645	10,643
Europe, The Middle East And Africa [Member] | Other Europe [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									83,147	79,910	78,201
Asia Pacific Region [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									196,270	169,250	166,660
Asia Pacific Region [Member] | Australia [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									52,871	49,274	58,448
Asia Pacific Region [Member] | Japan [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									51,544	43,171	44,132
Asia Pacific Region [Member] | China [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									48,257	40,619	34,674
Asia Pacific Region [Member] | Other Asia Pacific [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									$ 43,598	$ 36,186	$ 29,406