Segment and Geographic Information - Geographic Information Regarding Revenues (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues:
Total revenues	$ 827,028	$ 734,820	$ 2,459,122	$ 2,152,338
United States [Member]
Revenues:
Total revenues	518,100	487,990	1,515,384	1,343,342
United Kingdom [Member]
Revenues:
Total revenues	182,813	138,276	547,419	463,626
Asia [Member]
Revenues:
Total revenues	63,208	51,289	182,965	160,744
Other Europe/MEA [Member]
Revenues:
Total revenues	29,478	25,153	101,217	72,313
France [Member]
Revenues:
Total revenues	18,041	19,857	66,960	70,695
Other Americas [Member]
Revenues:
Total revenues	$ 15,388	$ 12,255	$ 45,177	$ 41,618