Consolidated Statements of Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenues (includes related party contra revenue of $163 and $0 for the three months ended March 31, 2019 and 2018, respectively)	$ 85,582	$ 81,061
Costs and operating expenses:
Cost of revenue (exclusive of depreciation and amortization presented separately below; includes related party cost of revenue of $134 and $0 for the three months ended March 31, 2019 and 2018, respectively)	8,936	7,452
Sales and marketing (includes related party expenses of $5,473 and $4,541 for the three months ended March 31, 2019 and 2018, respectively)	54,738	48,418
Technology and development	15,654	15,594
General and administrative	15,104	13,481
Depreciation and amortization	6,415	5,175
Total costs and operating expenses	100,847	90,120
Loss from operations	(15,265)	(9,059)
Interest income	1,001	604
Interest expense	0	(661)
Loss before income taxes	(14,264)	(9,116)
Provision for (benefit from) income taxes	101	(61)
Net loss	$ (14,365)	$ (9,055)
Net loss per share attributable to common stockholders:
Net loss per share, basic and diluted (in dollars per share)	$ (0.14)	$ (0.09)
Weighted average common shares outstanding, basic and diluted (in shares)	104,788	100,571
Other comprehensive loss:
Comprehensive loss	$ (14,365)	$ (9,055)