Revenue Recognition (Disaggregation of Revenue by Principal Geographic Area, Based on Customers' Domiciles) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue from Contract with Customer, Including Assessed Tax	$ 537,656	$ 462,021
United States [Member]
Revenue from Contract with Customer, Including Assessed Tax	327,461	288,613
Europe, the Middle East and Africa [Member]
Revenue from Contract with Customer, Including Assessed Tax	120,574	96,428
Asia Pacific Region [Member]
Revenue from Contract with Customer, Including Assessed Tax	56,039	48,952
Canada [Member]
Revenue from Contract with Customer, Including Assessed Tax	22,544	18,748
Latin America [Member]
Revenue from Contract with Customer, Including Assessed Tax	$ 11,038	$ 9,280