Segment Information (Schedule Of Revenue From Unaffiliated Customers By Geographic Area) (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) segment	Jun. 30, 2016 USD ($)
Number of reportable segments | segment			1
Revenue from unaffiliated customers	$ 159,467	$ 158,111	$ 315,898	$ 310,666
Operating Segments [Member]
Revenue from unaffiliated customers	159,467	158,111	315,898	310,666
Operating Segments [Member] | United States [Member]
Revenue from unaffiliated customers	80,921	76,369	158,793	153,018
Operating Segments [Member] | Other Americas [Member]
Revenue from unaffiliated customers	2,347	7,232	4,766	14,073
Operating Segments [Member] | Germany [Member]
Revenue from unaffiliated customers	20,331	20,547	40,147	39,429
Operating Segments [Member] | Other EMEA [Member]
Revenue from unaffiliated customers	33,118	28,207	66,260	56,756
Operating Segments [Member] | Asia Pacific [Member]
Revenue from unaffiliated customers	$ 22,750	$ 25,756	$ 45,932	$ 47,390