Consolidated Statements of Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement [Abstract]
Revenues	$ 72,405	$ 56,751	$ 196,250	$ 151,178
Costs and operating expenses:
Cost of revenue (exclusive of depreciation and amortization presented separately below; includes related party expenses of $0 and $405 for the nine months ended September 30, 2015 and 2014, respectively)	5,952	4,666	17,670	12,524
Sales and marketing (includes related party expenses of $7,701 and $6,700 for the three months ended September 30, 2015 and 2014, and $17,872 and $14,543 for the nine months ended September 30, 2015 and 2014, respectively)	43,969	36,399	116,135	97,458
Technology and development	12,340	10,906	33,079	26,751
General and administrative	16,467	14,919	53,643	42,873
Depreciation and amortization	4,477	3,388	12,521	9,474
Total costs and operating expenses	83,205	70,278	233,048	189,080
Loss from operations	(10,800)	(13,527)	(36,798)	(37,902)
Interest income	27	14	71	41
Interest expense	(159)	(27)	(322)	(327)
Other income	0	20	14	30
Loss before provision for income taxes	(10,932)	(13,520)	(37,035)	(38,158)
Provision for income taxes	173	120	432	437
Net loss	$ (11,105)	$ (13,640)	$ (37,467)	$ (38,595)
Net loss per share attributable to common stockholders:
Net loss per share, basic and diluted (in dollars per share)	$ (0.13)	$ (0.18)	$ (0.46)	$ (0.56)
Weighted average common shares outstanding, basic and diluted (in shares)	82,417	76,880	81,637	68,315
Other comprehensive loss:
Comprehensive loss	$ (11,105)	$ (13,640)	$ (37,467)	$ (38,595)