Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Revenue	$ 621,399	$ 584,065	$ 1,839,544	$ 1,723,925
Costs and operating expenses:
Cost of revenue (exclusive of amortization of acquired intangible assets shown below)	225,468	204,467	645,821	605,526
Research and development	57,226	42,341	162,761	120,873
Sales and marketing	120,220	102,626	353,218	308,060
General and administrative	124,523	113,320	363,050	323,141
Amortization of acquired intangible assets	7,753	6,598	23,075	20,025
Restructuring charges	332	2,948	3,303	10,236
Total costs and operating expenses	535,522	472,300	1,551,228	1,387,861
Income from operations	85,877	111,765	288,316	336,064
Interest income	4,463	3,809	13,368	10,522
Interest expense	(4,746)	(4,666)	(13,989)	(13,958)
Other income, net	535	778	414	1,004
Income before provision for income taxes	86,129	111,686	288,109	333,632
Provision for income taxes	25,617	35,686	88,895	109,139
Net income	$ 60,512	$ 76,000	$ 199,214	$ 224,493
Net income per share:
Basic (in dollars per share)	$ 0.35	$ 0.44	$ 1.16	$ 1.28
Diluted (in dollars per share)	$ 0.35	$ 0.43	$ 1.15	$ 1.27
Shares used in per share calculations:
Basic (in shares)	170,976	174,429	172,269	175,444
Diluted (in shares)	171,505	175,617	173,371	176,525