Consolidated Statements of Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Revenues	$ 82,440	$ 75,139	$ 240,016	$ 203,426
Costs and operating expenses:
Cost of revenue (exclusive of depreciation and amortization presented separately below)	7,088	6,320	20,610	18,910
Sales and marketing (includes related party expenses of $4,207 and $3,724 for the three months ended September 30, 2017 and 2016, and $12,750 and $10,384 for the nine months ended September 30, 2017 and 2016, respectively)	48,383	42,557	137,498	112,797
Technology and development	15,357	13,153	43,117	40,315
General and administrative	14,993	13,765	44,034	45,259
Depreciation and amortization	5,765	6,035	17,517	17,807
Total costs and operating expenses	91,586	81,830	262,776	235,088
Loss from operations	(9,146)	(6,691)	(22,760)	(31,662)
Interest income	402	91	784	286
Interest expense	(654)	(645)	(1,955)	(1,885)
Loss before provision for income taxes	(9,398)	(7,245)	(23,931)	(33,261)
Provision for income taxes	121	191	443	497
Net loss	$ (9,519)	$ (7,436)	$ (24,374)	$ (33,758)
Net loss per share attributable to common stockholders:
Net loss per share, basic and diluted (in dollars per share)	$ (0.10)	$ (0.09)	$ (0.26)	$ (0.40)
Weighted average common shares outstanding, basic and diluted (in shares)	98,665	84,822	93,108	84,075
Other comprehensive loss:
Comprehensive loss	$ (9,519)	$ (7,436)	$ (24,374)	$ (33,758)