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, 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
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 579,159	$ 551,030	$ 540,723	$ 526,536	$ 536,295	$ 498,042	$ 476,035	$ 453,502	$ 2,197,448	$ 1,963,874	$ 1,577,922
Cost of revenue (exclusive of amortization of acquired intangible assets)	193,212	183,204	179,910	169,294	163,201	158,812	149,318	139,612	725,620	610,943	511,087
Net income	$ 88,420	$ 88,040	$ 67,200	$ 77,746	$ 97,107	$ 91,155	$ 72,886	$ 72,800	$ 321,406	$ 333,948	$ 293,487
Basic net income per share (in dollars per share)	$ 0.50	$ 0.49	$ 0.38	$ 0.44	$ 0.55	$ 0.51	$ 0.41	$ 0.41	$ 1.80	$ 1.87	$ 1.65
Diluted net income per share (in dollars per share)	$ 0.49	$ 0.49	$ 0.37	$ 0.43	$ 0.54	$ 0.50	$ 0.40	$ 0.40	$ 1.78	$ 1.84	$ 1.61