Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Revenue		$ 993,260	$ 992,065	$ 882,513
Cost of revenue	[1]	486,804	483,900	425,083
Gross profit		506,456	508,165	457,430
Operating expenses:
Research and development	[1]	157,358	151,395	141,364
Sales and marketing	[1]	173,697	169,042	156,339
General and administrative	[1]	92,953	85,618	72,797
Amortization of identified intangibles		47,339	39,560	26,510
Restructuring and other (Note 13)		7,562	6,731	5,731
Total operating expenses		478,909	452,346	402,741
Income from operations		27,547	55,819	54,689
Interest expense		(19,505)	(17,716)	(17,364)
Interest income and other income (expense), net		4,088	545	(1,757)
Income before income taxes		12,130	38,648	35,568
Benefit from (provision for) income taxes		(27,475)	6,301	(3,369)
Net income (loss)		$ (15,345)	$ 44,949	$ 32,199
Net income (loss) per basic common share		$ (0.33)	$ 0.96	$ 0.68
Net income (loss) per diluted common share		$ (0.33)	$ 0.94	$ 0.67
Shares used in basic per-share calculation		46,281	46,900	47,217
Shares used in diluted per-share calculation		46,281	47,797	48,150

[1] Includes stock-based compensation expense as follows: 2017 2016 2015 Cost of revenue $ 2,561 $ 2,784 $ 2,837 Research and development 9,177 8,968 9,406 Sales and marketing 6,583 7,690 7,602 General and administrative 8,211 12,384 14,226