CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenue	$ 96,748	$ 78,015	$ 267,475	$ 220,274
Cost of revenue	26,596	22,494	75,489	65,207
Gross profit	70,152	55,521	191,986	155,067
Operating expenses
Research and development	20,833	16,209	60,728	47,705
Sales and marketing	33,577	25,322	98,695	70,319
General and administrative	18,047	16,468	52,973	46,193
Provision for transaction losses	724	1,214	2,654	2,706
Total operating expenses	73,181	59,213	215,050	166,923
Loss from operations	(3,029)	(3,692)	(23,064)	(11,856)
Interest expense	152	317	640	1,047
Other (income) expense, net	(452)	(462)	31	(1,773)
Loss before income taxes	(2,729)	(3,547)	(23,735)	(11,130)
Income tax provision	(18)	0	(57)	(28)
Net loss	$ (2,747)	$ (3,547)	$ (23,792)	$ (11,158)
Net loss per share, basic and diluted (in dollars per share)	$ (0.02)	$ (0.03)	$ (0.20)	$ (0.10)
Weighted-average shares used to compute net loss per share, basic and diluted (in shares)	120,680,797	111,163,396	117,120,815	108,844,495