Quarterly Financial Results (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 772,123	$ 709,912	$ 705,074	$ 706,508	$ 713,363	$ 669,628	$ 662,759	$ 688,724	$ 2,893,617	$ 2,714,474	$ 2,489,035
Cost of revenue (exclusive of amortization of acquired intangible assets shown below)	257,750	246,938	242,193	240,743	243,927	239,246	235,487	234,825	987,624	953,485	875,837
Net income	$ 119,100	$ 137,890	$ 113,915	$ 107,130	$ 94,015	$ 107,583	$ 43,061	$ 53,714	$ 478,035	$ 298,373	$ 222,766
Basic net income per share (in dollars per share)	$ 0.74	$ 0.85	$ 0.70	$ 0.66	$ 0.58	$ 0.65	$ 0.25	$ 0.32	$ 2.94	$ 1.78	$ 1.30
Diluted net income per share (in dollars per share)	$ 0.73	$ 0.84	$ 0.69	$ 0.65	$ 0.57	$ 0.64	$ 0.25	$ 0.31	$ 2.90	$ 1.76	$ 1.29