Revenue Recognition (Disaggregation of Revenue by Principal Geographic Area, Based on Customers' Domiciles) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Total revenue	$ 620,103	$ 580,752	$ 1,196,159	$ 1,118,408
United States
Disaggregation of Revenue [Line Items]
Total revenue	388,875	356,736	747,163	684,197
Europe, the Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenue	124,840	122,270	246,586	242,844
Asia Pacific Region
Disaggregation of Revenue [Line Items]
Total revenue	64,033	62,505	124,108	118,544
Canada
Disaggregation of Revenue [Line Items]
Total revenue	27,654	26,407	50,878	48,951
Latin America
Disaggregation of Revenue [Line Items]
Total revenue	$ 14,701	$ 12,834	$ 27,424	$ 23,872