Segment Information (Schedule of Revenue From Unaffiliated Customers By Geographic Area) (Details) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Number of reportable segments | segment													1
Revenue	$ 180,712	$ 164,511	$ 176,568	$ 165,869	$ 177,264	$ 152,907	$ 159,467	$ 156,431	$ 165,937	$ 156,362	$ 158,111	$ 152,555	$ 687,660	$ 646,069	$ 632,965
Consolidated Revenue | Customer Concentration Risk | Customer One
Concentration risk (as a percentage)													13.00%
United States
Revenue													$ 332,611	322,399	329,553
Other Americas
Revenue													8,154	11,377	11,332
EMEA
Revenue													237,462	220,357	193,141
Asia Pacific
Revenue													$ 109,433	$ 91,936	$ 98,939