Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Statement [Abstract]
Revenue	$ 572,135	$ 540,723	$ 1,139,860	$ 1,067,259
Costs and operating expenses:
Cost of revenue (exclusive of amortization of acquired intangible assets shown below)	206,323	179,910	401,059	349,204
Research and development	37,690	36,693	78,532	72,521
Sales and marketing	103,223	111,501	205,434	214,980
General and administrative	107,538	99,152	209,821	188,744
Amortization of acquired intangible assets	6,711	6,752	13,427	13,532
Restructuring charges	470	455	7,288	497
Total costs and operating expenses	461,955	434,463	915,561	839,478
Income from operations	110,180	106,260	224,299	227,781
Interest income	3,393	2,541	6,713	5,542
Interest expense	(4,639)	(4,678)	(9,292)	(9,254)
Other income (expense), net	415	(1,605)	226	(1,906)
Income before provision for income taxes	109,349	102,518	221,946	222,163
Provision for income taxes	35,714	35,318	73,453	77,217
Net income	$ 73,635	$ 67,200	$ 148,493	$ 144,946
Net income per share:
Basic (in dollars per share)	$ 0.42	$ 0.38	$ 0.84	$ 0.81
Diluted (in dollars per share)	$ 0.42	$ 0.37	$ 0.84	$ 0.80
Shares used in per share calculations:
Basic (in shares)	175,499	178,682	175,951	178,614
Diluted (in shares)	176,420	180,738	176,980	180,782