Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Revenue	$ 669,628	$ 624,440	$ 2,001,111	$ 1,830,565
Costs and operating expenses:
Cost of revenue (exclusive of amortization of acquired intangible assets shown below)	239,246	225,490	709,558	645,897
Research and development	61,049	57,226	185,823	162,761
Sales and marketing	125,323	117,863	379,556	350,299
General and administrative	119,911	124,523	444,502	363,050
Amortization of acquired intangible assets	8,294	7,753	25,019	23,075
Restructuring (benefit) charges	(732)	332	14,442	3,303
Total costs and operating expenses	553,091	533,187	1,758,900	1,548,385
Income from operations	116,537	91,253	242,211	282,180
Interest income	9,258	4,463	19,632	13,368
Interest expense	(14,566)	(4,746)	(28,620)	(13,989)
Other (expense) income, net	(459)	535	(3,207)	414
Income before provision for income taxes	110,770	91,505	230,016	281,973
Provision for income taxes	3,187	27,594	25,658	86,727
Net income	$ 107,583	$ 63,911	$ 204,358	$ 195,246
Net income per share:
Basic (in dollars per share)	$ 0.65	$ 0.37	$ 1.21	$ 1.13
Diluted (in dollars per share)	$ 0.64	$ 0.37	$ 1.20	$ 1.13
Shares used in per share calculations:
Basic (in shares)	165,924	170,976	168,763	172,269
Diluted (in shares)	167,900	171,505	170,732	173,371