Revenue Recognition (Disaggregation of Revenue by Principal Geographic Area, Based on Customers' Domiciles) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Total revenue	$ 605,303	$ 545,448	$ 1,801,462	$ 1,663,856
United States
Disaggregation of Revenue [Line Items]
Total revenue	380,184	340,692	1,127,347	1,024,889
Europe, the Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenue	122,050	112,466	368,636	355,310
Asia Pacific Region
Disaggregation of Revenue [Line Items]
Total revenue	64,648	56,954	188,756	175,498
Canada
Disaggregation of Revenue [Line Items]
Total revenue	24,334	22,459	75,212	71,410
Latin America
Disaggregation of Revenue [Line Items]
Total revenue	$ 14,087	$ 12,877	$ 41,511	$ 36,749