Revenue Revenue - Statement of Operations (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue from External Customer [Line Items]
Revenue		$ 261,072	$ 247,047	$ 500,938	$ 475,738
Cost of revenue	[1]	132,484	119,795	253,243	224,956
Gross profit		128,588	127,252	247,695	250,782
Operating expenses		114,944	119,261	236,116	234,648
Income from operations		13,644	7,991	11,579	16,134
Interest income and other income (expense), net		(355)	755	934	1,042
Income before income taxes		8,300	3,780	2,570	7,550
Provision for income taxes		(4,532)	(1,021)	(2,397)	(4)
Net income		3,768	$ 2,759	173	$ 7,546
Amounts in Accordance with ASC 606
Revenue from External Customer [Line Items]
Revenue		261,072		500,938
Cost of revenue		132,484		253,243
Gross profit		128,588		247,695
Operating expenses		114,944		236,116
Income from operations		13,644		11,579
Interest income and other income (expense), net		(355)		934
Income before income taxes		8,300		2,570
Provision for income taxes		(4,532)		(2,397)
Net income		3,768		173
Amounts in Accordance with ASC 605
Revenue from External Customer [Line Items]
Revenue		260,195		498,602
Cost of revenue		132,625		253,442
Gross profit		127,570		245,160
Operating expenses		115,069		236,102
Income from operations		12,501		9,058
Interest income and other income (expense), net		(490)		624
Income before income taxes		7,022		(261)
Provision for income taxes		(4,386)		(2,102)
Net income		2,636		(2,363)
Difference between Revenue Guidance in Effect before and after Topic 605, 606 [Member] | Effect of change higher (lower)
Revenue from External Customer [Line Items]
Revenue		877		2,336
Cost of revenue		(141)		(199)
Gross profit		1,018		2,535
Operating expenses		(125)		14
Income from operations		1,143		2,521
Interest income and other income (expense), net		135		310
Income before income taxes		1,278		2,831
Provision for income taxes		(146)		(295)
Net income		$ 1,132		$ 2,536

[1] Includes stock-based compensation expense as follows: Three Months EndedJune 30, Six Months Ended June 30, 2018 2017 2018 2017Cost of revenue$1,043 $665 $1,811 $1,499Research and development3,513 2,346 5,868 5,916Sales and marketing2,591 1,773 4,390 4,068General and administrative4,638 2,829 6,486 6,410