Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Revenue		$ 247,047	$ 245,650	$ 475,738	$ 479,783
Cost of revenue	[1]	119,795	120,603	224,956	236,339
Gross profit		127,252	125,047	250,782	243,444
Operating expenses:
Research and development	[1]	38,989	37,676	78,616	74,798
Sales and marketing	[1]	43,714	42,770	86,749	84,300
General and administrative	[1]	21,135	21,446	42,164	42,278
Restructuring and other (Note 11)		3,671	1,710	4,589	4,425
Amortization of identified intangibles		11,752	9,736	22,530	18,965
Total operating expenses		119,261	113,338	234,648	224,766
Income from operations		7,991	11,709	16,134	18,678
Interest expense		(4,966)	(4,375)	(9,626)	(8,733)
Interest income and other income, net		755	420	1,042	199
Income before income taxes		3,780	7,754	7,550	10,144
Provision for income taxes		(1,021)	(2,519)	(4)	(2,806)
Net income		$ 2,759	$ 5,235	$ 7,546	$ 7,338
Net income per basic common share		$ 0.06	$ 0.11	$ 0.16	$ 0.16
Net income per diluted common share		$ 0.06	$ 0.11	$ 0.16	$ 0.15
Shares used in basic per-share calculation		46,429	46,943	46,490	47,079
Shares used in diluted per-share calculation		47,150	47,830	47,199	47,930

[1] Includes stock-based compensation expense as follows: 2017 2016 2017 2016 Cost of revenue $ 665 $ 534 $ 1,499 $ 1,231 Research and development 2,346 1,886 5,916 4,926 Sales and marketing 1,773 1,550 4,068 3,899 General and administrative 2,829 3,135 6,410 8,334