Consolidated Statements of Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Revenues	$ 87,850	$ 81,819	$ 168,911	$ 157,576
Costs and operating expenses:
Cost of revenue (exclusive of depreciation and amortization presented separately below)	7,752	7,130	15,204	13,522
Sales and marketing (includes related party expenses of $5,277 and $4,487 for the three months ended June 30, 2018 and 2017, and $9,818 and $8,543 for the six months ended June 30, 2018 and 2017, respectively)	52,014	46,933	100,432	89,115
Technology and development	15,694	14,131	31,288	27,760
General and administrative	13,494	15,413	26,975	29,041
Depreciation and amortization	5,641	5,668	10,816	11,752
Total costs and operating expenses	94,595	89,275	184,715	171,190
Loss from operations	(6,745)	(7,456)	(15,804)	(13,614)
Interest income	750	249	1,354	382
Interest expense	(662)	(652)	(1,323)	(1,301)
Loss before income taxes	(6,657)	(7,859)	(15,773)	(14,533)
(Benefit from) / provision for income taxes	(35)	201	(96)	322
Net loss	$ (6,622)	$ (8,060)	$ (15,677)	$ (14,855)
Net loss per share attributable to common stockholders:
Net loss per share, basic and diluted (in dollars per share)	$ (0.07)	$ (0.09)	$ (0.16)	$ (0.16)
Weighted average common shares outstanding, basic and diluted (in shares)	101,150	93,745	100,862	90,283
Other comprehensive loss:
Comprehensive loss	$ (6,622)	$ (8,060)	$ (15,677)	$ (14,855)