Condensed Consolidated Statements of Operations - 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		$ 248,359	$ 245,575	$ 724,097	$ 725,358
Cost of revenue	[1]	120,901	120,381	345,858	356,720
Gross profit		127,458	125,194	378,239	368,638
Operating expenses:
Research and development	[1]	39,585	36,933	118,201	111,731
Sales and marketing	[1]	42,269	43,060	129,018	127,360
General and administrative	[1]	25,075	24,088	67,239	66,366
Restructuring and other (Note 11)		833	1,308	5,421	5,733
Amortization of identified intangibles		12,299	10,395	34,829	29,360
Total operating expenses		120,061	115,784	354,708	340,550
Income from operations		7,397	9,410	23,531	28,088
Interest expense		(4,912)	(4,510)	(14,538)	(13,243)
Interest income and other income, net		1,760	915	2,802	1,114
Income before income taxes		4,245	5,815	11,795	15,959
Benefit from (provision for) income taxes		(791)	11,847	(795)	9,041
Net income		$ 3,454	$ 17,662	$ 11,000	$ 25,000
Net income per basic common share		$ 0.07	$ 0.38	$ 0.24	$ 0.53
Net income per diluted common share		$ 0.07	$ 0.37	$ 0.23	$ 0.52
Shares used in basic per-share calculation		46,348	46,794	46,442	46,983
Shares used in diluted per-share calculation		46,937	47,621	47,102	47,791

[1] Includes stock-based compensation expense as follows: 2017 2016 2017 2016 Cost of revenue $ 486 $ 642 $ 1,985 $ 1,873 Research and development 1,640 2,061 7,556 6,987 Sales and marketing 1,108 2,260 5,176 6,159 General and administrative 1,414 3,590 7,824 11,923