Quarterly Financial Results (unaudited) - Schedule of Quarterly Financial Results (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 713,363	$ 669,628	$ 662,759	$ 668,724	$ 658,470	$ 624,440	$ 605,832	$ 600,293	$ 2,714,474	$ 2,489,035	$ 2,347,988
Cost of revenue (exclusive of amortization of acquired intangible assets shown below)	243,927	239,246	235,487	234,825	229,940	225,490	214,680	205,727	953,485	875,837	809,106
Net income	$ 94,015	$ 107,583	$ 43,061	$ 53,714	$ 27,520	$ 63,911	$ 56,752	$ 74,583	$ 298,373	$ 222,766	$ 320,727
Basic net income per share (in dollars per share)	$ 0.58	$ 0.65	$ 0.25	$ 0.32	$ 0.16	$ 0.37	$ 0.33	$ 0.43	$ 1.78	$ 1.30	$ 1.83
Diluted net income per share (in dollars per share)	$ 0.57	$ 0.64	$ 0.25	$ 0.31	$ 0.16	$ 0.37	$ 0.33	$ 0.43	$ 1.76	$ 1.29	$ 1.82