Revenue Recognition (Disaggregation of Revenue by Principal Geographic Area, Based on Customers' Domiciles) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Total revenue	$ 549,386	$ 545,448	$ 580,752	$ 537,656	$ 506,121	$ 491,976	$ 508,940	$ 462,021	$ 2,213,242	$ 1,969,058	$ 1,775,423
United States
Disaggregation of Revenue [Line Items]
Total revenue									1,357,909	1,203,547	1,089,595
Canada
Disaggregation of Revenue [Line Items]
Total revenue									94,206	83,818	74,923
Latin America
Disaggregation of Revenue [Line Items]
Total revenue									50,969	46,893	38,872
Americas
Disaggregation of Revenue [Line Items]
Total revenue									1,503,084	1,334,258	1,203,390
Germany
Disaggregation of Revenue [Line Items]
Total revenue									100,459	88,328	80,156
United Kingdom
Disaggregation of Revenue [Line Items]
Total revenue									87,807	80,149	77,671
France
Disaggregation of Revenue [Line Items]
Total revenue									60,319	55,993	51,204
Italy
Disaggregation of Revenue [Line Items]
Total revenue									36,956	31,889	28,907
Spain
Disaggregation of Revenue [Line Items]
Total revenue									33,687	28,866	24,268
Switzerland
Disaggregation of Revenue [Line Items]
Total revenue									19,875	17,913	16,361
Netherlands
Disaggregation of Revenue [Line Items]
Total revenue									18,090	15,877	14,049
Other
Disaggregation of Revenue [Line Items]
Total revenue									114,877	100,409	83,147
Europe, the Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenue									472,070	419,424	375,763
Australia
Disaggregation of Revenue [Line Items]
Total revenue									63,386	56,994	52,871
China
Disaggregation of Revenue [Line Items]
Total revenue									57,621	55,810	48,257
Japan
Disaggregation of Revenue [Line Items]
Total revenue									60,213	53,344	51,544
Other
Disaggregation of Revenue [Line Items]
Total revenue									56,868	49,228	43,598
Asia Pacific Region
Disaggregation of Revenue [Line Items]
Total revenue									$ 238,088	$ 215,376	$ 196,270