CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenue	$ 87,531	$ 73,783	$ 170,727	$ 142,259
Cost of revenue	25,408	21,588	48,893	42,713
Gross profit	62,123	52,195	121,834	99,546
Operating expenses
Research and development	20,547	15,696	39,895	31,496
Sales and marketing	34,440	24,479	65,118	44,997
General and administrative	17,102	14,064	34,926	29,725
Provision for transaction losses	1,018	855	1,930	1,492
Total operating expenses	73,107	55,094	141,869	107,710
Loss from operations	(10,984)	(2,899)	(20,035)	(8,164)
Interest expense	258	357	488	730
Other (income) expense, net	(248)	(832)	483	(1,311)
Loss before income taxes	(10,994)	(2,424)	(21,006)	(7,583)
Income tax provision	(30)	(27)	(39)	(28)
Net loss	$ (11,024)	$ (2,451)	$ (21,045)	$ (7,611)
Net loss per share, basic and diluted (in dollars per share)	$ (0.09)	$ (0.02)	$ (0.18)	$ (0.07)
Weighted-average shares used to compute net loss per share, basic and diluted (in shares)	116,523,570	108,683,099	115,321,264	107,665,492