Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Revenue	$ 2,502,996	$ 2,340,049	$ 2,197,448
Costs and operating expenses:
Cost of revenue (exclusive of amortization of acquired intangible assets shown below)	875,758	809,001	725,620
Research and development	222,434	167,628	148,591
Sales and marketing	493,632	426,967	440,988
General and administrative	509,165	439,916	388,265
Amortization of acquired intangible assets	30,904	26,642	27,067
Restructuring charges	54,884	10,301	767
Total costs and operating expenses	2,186,777	1,880,455	1,731,298
Income from operations	316,219	459,594	466,150
Interest income	17,855	14,702	11,200
Interest expense	(18,839)	(18,638)	(18,525)
Other income (expense), net	887	3,788	(2,201)
Income before provision for income taxes	316,122	459,446	456,624
Provision for income taxes	97,801	143,314	135,218
Net income	$ 218,321	$ 316,132	$ 321,406
Net income per share:
Basic (in dollars per share)	$ 1.27	$ 1.81	$ 1.80
Diluted (in dollars per share)	$ 1.26	$ 1.79	$ 1.78
Shares used in per share calculations:
Basic (in shares)	171,559	174,917	178,391
Diluted (in shares)	172,711	176,215	180,415