Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Revenue	$ 584,065	$ 551,030	$ 1,723,925	$ 1,618,289
Costs and operating expenses:
Cost of revenue (exclusive of amortization of acquired intangible assets shown below)	204,467	183,204	605,526	532,408
Research and development	42,341	38,396	120,873	110,917
Sales and marketing	102,626	107,426	308,060	322,406
General and administrative	113,320	99,543	323,141	288,287
Amortization of acquired intangible assets	6,598	6,752	20,025	20,284
Restructuring charges	2,948	20	10,236	517
Total costs and operating expenses	472,300	435,341	1,387,861	1,274,819
Income from operations	111,765	115,689	336,064	343,470
Interest income	3,809	2,723	10,522	8,265
Interest expense	(4,666)	(4,630)	(13,958)	(13,884)
Other income (expense), net	778	204	1,004	(1,702)
Income before provision for income taxes	111,686	113,986	333,632	336,149
Provision for income taxes	35,686	25,946	109,139	103,163
Net income	$ 76,000	$ 88,040	$ 224,493	$ 232,986
Net income per share:
Basic (in dollars per share)	$ 0.44	$ 0.49	$ 1.28	$ 1.30
Diluted (in dollars per share)	$ 0.43	$ 0.49	$ 1.27	$ 1.29
Shares used in per share calculations:
Basic (in shares)	174,429	178,547	175,444	178,591
Diluted (in shares)	175,617	180,364	176,525	180,642