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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 616,124	$ 584,065	$ 572,135	$ 567,725	$ 579,159	$ 551,030	$ 540,723	$ 526,536	$ 2,340,049	$ 2,197,448	$ 1,963,874
Cost of revenue (exclusive of amortization of acquired intangible assets)	203,475	204,467	206,323	194,736	193,212	183,204	179,910	169,294	809,001	725,620	610,943
Net income	$ 91,639	$ 76,000	$ 73,635	$ 74,858	$ 88,420	$ 88,040	$ 67,200	$ 77,746	$ 316,132	$ 321,406	$ 333,948
Basic net income per share (in dollars per share)	$ 0.53	$ 0.44	$ 0.42	$ 0.42	$ 0.50	$ 0.49	$ 0.38	$ 0.44	$ 1.81	$ 1.80	$ 1.87
Diluted net income per share (in dollars per share)	$ 0.52	$ 0.43	$ 0.42	$ 0.42	$ 0.49	$ 0.49	$ 0.37	$ 0.43	$ 1.79	$ 1.78	$ 1.84