Consolidated Statements of Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Revenues	$ 81,819	$ 66,427	$ 157,576	$ 128,287
Costs and operating expenses:
Cost of revenue (exclusive of depreciation and amortization presented separately below)	7,130	6,365	13,522	12,590
Sales and marketing (includes related party expenses of $4,487 and $3,359 for the three months ended June 30, 2017 and 2016, and $8,543 and $6,660 for the six months ended June 30, 2017 and 2016, respectively)	46,933	38,129	89,115	70,240
Technology and development	14,131	14,022	27,760	27,162
General and administrative	15,413	15,998	29,041	31,494
Depreciation and amortization	5,668	5,868	11,752	11,772
Total costs and operating expenses	89,275	80,382	171,190	153,258
Loss from operations	(7,456)	(13,955)	(13,614)	(24,971)
Interest income	249	102	382	195
Interest expense	(652)	(632)	(1,301)	(1,240)
Loss before provision for income taxes	(7,859)	(14,485)	(14,533)	(26,016)
Provision for income taxes	201	170	322	306
Net loss	$ (8,060)	$ (14,655)	$ (14,855)	$ (26,322)
Net loss per share attributable to common stockholders:
Net loss per share, basic and diluted (in dollars per share)	$ (0.09)	$ (0.17)	$ (0.16)	$ (0.31)
Weighted average common shares outstanding, basic and diluted (in shares)	93,745	83,931	90,283	83,697
Other comprehensive loss:
Comprehensive loss	$ (8,060)	$ (14,655)	$ (14,855)	$ (26,322)