Segment and Geographic Information - Geographic Information Regarding Revenues (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenues:
Total revenues	$ 737,757	$ 653,770	$ 1,445,187	$ 1,294,424
United States [Member]
Revenues:
Total revenues	424,454	375,430	810,377	732,258
United Kingdom [Member]
Revenues:
Total revenues	177,796	161,659	364,606	325,350
Asia [Member]
Revenues:
Total revenues	58,648	52,704	119,757	109,455
Other Europe/MEA [Member]
Revenues:
Total revenues	37,737	23,950	71,739	47,160
France [Member]
Revenues:
Total revenues	23,654	25,271	48,919	50,838
Other Americas [Member]
Revenues:
Total revenues	$ 15,468	$ 14,756	$ 29,789	$ 29,363