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Revenue by Geographic Area (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Schedule Of Geographical Information [Line Items]      
Total revenues $ 1,854,658 $ 1,741,301 $ 1,629,838
Americas Principally U S      
Schedule Of Geographical Information [Line Items]      
Total revenues 871,297 847,458 791,568
Europe      
Schedule Of Geographical Information [Line Items]      
Total revenues 674,987 627,524 595,850
Asia-Pacific, Middle-East and Africa      
Schedule Of Geographical Information [Line Items]      
Total revenues $ 308,374 $ 266,319 $ 242,420