CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenue	$ 73,941	$ 50,070	$ 203,092	$ 137,175
Cost of revenue	16,033	11,209	45,225	30,581
Gross profit	57,908	38,861	157,867	106,594
Operating expenses:
Sales and marketing	45,538	24,462	112,191	66,206
Research and development	27,863	14,827	64,380	39,113
General and administrative	25,593	36,040	59,300	69,081
Total operating expenses	98,994	75,329	235,871	174,400
Loss from operations	(41,086)	(36,468)	(78,004)	(67,806)
Non-operating income (expense):
Interest income	1,079	387	2,822	847
Interest expense	(407)	(251)	(970)	(726)
Other expense, net	(651)	(1,240)	(1,030)	(1,903)
Total non-operating income (expense), net	21	(1,104)	822	(1,782)
Loss before income taxes	(41,065)	(37,572)	(77,182)	(69,588)
Provision for (benefit from) income taxes	(212)	417	491	889
Net loss	$ (40,853)	$ (37,989)	$ (77,673)	$ (70,477)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.35)	$ (0.47)	$ (0.81)	$ (0.88)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (in shares)	118,056	81,579	96,393	79,755