CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenue	$ 216,113	$ 164,203	$ 516,128	$ 445,114
Type of Revenue [Extensible List]	us-gaap:ServiceMember	us-gaap:ServiceMember	us-gaap:ServiceMember	us-gaap:ServiceMember
Operating expenses:
Platform operations	$ 44,826	$ 39,932	$ 127,167	$ 108,913
Type of Cost, Good or Service [Extensible List]	us-gaap:ServiceMember	us-gaap:ServiceMember	us-gaap:ServiceMember	us-gaap:ServiceMember
Sales and marketing	$ 44,637	$ 36,142	$ 116,002	$ 89,951
Technology and development	41,079	29,185	117,931	83,949
General and administrative	42,789	37,017	117,252	102,755
Total operating expenses	173,331	142,276	478,352	385,568
Income from operations	42,782	21,927	37,776	59,546
Other expense (income):
Interest expense (income), net	235	(1,480)	(740)	(3,763)
Foreign currency exchange (gain) loss, net	(12)	(412)	1,574	784
Total other expense (income), net	223	(1,892)	834	(2,979)
Income before income taxes	42,559	23,819	36,942	62,525
Provision for (benefit from) income taxes	1,312	4,397	(53,473)	5,152
Net income	$ 41,247	$ 19,422	$ 90,415	$ 57,373
Earnings per share:
Basic	$ 0.89	$ 0.43	$ 1.96	$ 1.29
Diluted	$ 0.84	$ 0.40	$ 1.86	$ 1.20
Weighted average shares outstanding:
Basic	46,582	44,771	46,075	44,363
Diluted	49,220	48,037	48,731	47,728