CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenue	$ 201,911	$ 131,359
Costs and expenses:
Cost of revenue	73,694	51,653
Research and development	72,444	60,047
Sales and marketing	76,394	55,774
General and administrative	24,205	18,867
Total costs and expenses	246,737	186,341
Loss from operations	(44,826)	(54,982)
Other income (expense), net:
Interest income	4,059	2,638
Interest expense and other income (expense), net	(500)	(242)
Loss before provision for income taxes	(41,267)	(52,586)
Provision for income taxes	153	123
Net loss	$ (41,420)	$ (52,709)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.33)	$ (0.42)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)	127,346	126,857