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	$ 481,985	$ 423,124	$ 339,651
Cost of revenue	142,867	135,752	109,864
Gross profit	339,118	287,372	229,787
Operating expenses:
Sales and marketing	240,271	225,631	207,026
Research and development	61,975	46,977	40,991
General and administrative	84,589	70,956	49,877
Restructuring	1,539	0	0
Amortization of certain acquired intangible assets	0	150	600
Total operating expenses	388,374	343,714	298,494
Loss from operations	(49,256)	(56,342)	(68,707)
Other income (expense):
Interest income	2,951	1,702	894
Interest expense	(14,762)	(12,924)	(12,506)
Other, net	1,478	1,934	(4,016)
Other income (expense), net	(10,333)	(9,288)	(15,628)
Loss before income tax provision	(59,589)	(65,630)	(84,335)
Income tax provision	(1,746)	(1,207)	(1,181)
Net loss	$ (61,335)	$ (66,837)	$ (85,516)
Net loss per share — basic and diluted (usd per share)	$ (1.07)	$ (1.20)	$ (1.58)
Weighted average common shares outstanding, basic and diluted (in shares)	57,262	55,595	54,171