Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Income Statement [Abstract]
Revenue	$ 567,725	$ 526,536
Costs and operating expenses:
Cost of revenue (exclusive of amortization of acquired intangible assets shown below)	194,736	169,294
Research and development	40,842	35,828
Sales and marketing	102,211	103,479
General and administrative	102,283	89,592
Amortization of acquired intangible assets	6,716	6,780
Restructuring charges	6,818	42
Total costs and operating expenses	453,606	405,015
Income from operations	114,119	121,521
Interest income	3,320	3,001
Interest expense	(4,653)	(4,576)
Other expense, net	(189)	(301)
Income before provision for income taxes	112,597	119,645
Provision for income taxes	37,739	41,899
Net income	$ 74,858	$ 77,746
Net income per share:
Basic (in dollars per share)	$ 0.42	$ 0.44
Diluted (in dollars per share)	$ 0.42	$ 0.43
Shares used in per share calculations:
Basic (in shares)	176,403	178,545
Diluted (in shares)	177,539	180,825