CONDENSED CONSOLIDATED STATEMENTS OF INCOME - 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	$ 164,203	$ 118,825	$ 445,114	$ 316,826
Type of Revenue [Extensible List]	us-gaap:ServiceMember	us-gaap:ServiceMember	us-gaap:ServiceMember	us-gaap:ServiceMember
Operating expenses:
Platform operations	$ 39,932	$ 29,344	$ 108,913	$ 78,842
Type of Cost, Good or Service [Extensible List]	us-gaap:ServiceMember	us-gaap:ServiceMember	us-gaap:ServiceMember	us-gaap:ServiceMember
Sales and marketing	$ 36,142	$ 23,287	$ 89,951	$ 60,007
Technology and development	29,185	22,621	83,949	59,806
General and administrative	37,017	21,310	102,755	59,816
Total operating expenses	142,276	96,562	385,568	258,471
Income from operations	21,927	22,263	59,546	58,355
Other expense (income):
Interest expense (income), net	(1,480)	(237)	(3,763)	(113)
Foreign currency exchange (gain) loss, net	(412)	395	784	2,035
Total other expense (income), net	(1,892)	158	(2,979)	1,922
Income before income taxes	23,819	22,105	62,525	56,433
Provision for income taxes	4,397	1,813	5,152	7,728
Net income	$ 19,422	$ 20,292	$ 57,373	$ 48,705
Earnings per share:
Basic	$ 0.43	$ 0.47	$ 1.29	$ 1.15
Diluted	$ 0.40	$ 0.44	$ 1.20	$ 1.07
Weighted average shares outstanding:
Basic	44,771	42,721	44,363	42,178
Diluted	48,037	46,576	47,728	45,460