Schedule of Revenue by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues from External Customers and Long-Lived Assets
Revenue	$ 1,748,919	$ 1,831,732	$ 1,838,070	$ 1,773,912	$ 1,684,131	$ 1,721,024	$ 1,709,132	$ 1,625,777	$ 7,192,633	$ 6,740,064	$ 5,062,528
United States
Revenues from External Customers and Long-Lived Assets
Revenue									4,831,875	4,499,743	3,544,360
United Kingdom
Revenues from External Customers and Long-Lived Assets
Revenue									1,382,432	1,321,786	981,585
Other countries
Revenues from External Customers and Long-Lived Assets
Revenue									$ 978,326	$ 918,535	$ 536,583