Segment and Geographic Information - Geographic Information Regarding Revenues (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues:
Total revenues	$ 960,076	$ 848,901	$ 1,916,722	$ 1,632,094
United States [Member]
Revenues:
Total revenues	595,986	535,598	1,168,240	997,284
United Kingdom [Member]
Revenues:
Total revenues	205,801	177,796	429,360	364,606
Asia [Member]
Revenues:
Total revenues	70,129	58,648	139,158	119,757
Other Europe/MEA [Member]
Revenues:
Total revenues	49,665	37,737	103,337	71,739
France [Member]
Revenues:
Total revenues	22,712	23,654	45,730	48,919
Other Americas [Member]
Revenues:
Total revenues	$ 15,783	$ 15,468	$ 30,897	$ 29,789