Segment and Geographic Information - Geographic Information Regarding Revenues (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Total revenues	$ 977,254	$ 827,028	$ 2,893,976	$ 2,459,122
United States [Member]
Revenues:
Total revenues	637,939	518,100	1,806,179	1,515,384
United Kingdom [Member]
Revenues:
Total revenues	191,683	182,813	621,043	547,419
Asia [Member]
Revenues:
Total revenues	71,077	63,208	210,235	182,965
Other Europe/MEA [Member]
Revenues:
Total revenues	43,655	29,478	146,992	101,217
France [Member]
Revenues:
Total revenues	17,140	18,041	62,870	66,960
Other Americas [Member]
Revenues:
Total revenues	$ 15,760	$ 15,388	$ 46,657	$ 45,177