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		$ 430,492	$ 311,999	$ 208,768
Cost of revenue	[1]	127,422	93,900	67,184
Gross profit		303,070	218,099	141,584
Operating expenses:
Research and development	[1]	115,291	91,067	62,615
Sales and marketing	[1]	220,742	166,987	114,052
General and administrative	[1]	81,680	64,371	47,902
Total operating expenses	[1]	417,713	322,425	224,569
Operating loss		(114,643)	(104,326)	(82,985)
Other income (expense), net		2,487	1,520	(729)
Loss before provision for (benefit from) income taxes		(112,156)	(102,806)	(83,714)
Provision for (benefit from) income taxes		(1,518)	993	338
Net loss		$ (110,638)	$ (103,799)	$ (84,052)
Net loss per, basic and diluted (usd per share)		$ (1.11)	$ (1.11)	$ (0.99)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted (in shares)		99,918	93,161	84,926

[1] Includes share-based compensation expense as follows as of December 31, 2017, 2016, and 2015:Cost of revenue: $9,040, $7,045, $4,541Research and development: $29,970, $27,083, $19,414Sales and marketing: $24,776, $23,043, $14,759General and administrative: $21,263, $16,608, $13,842