Consolidated Statements of Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Revenues (includes related party contra revenue of $345 and $0 for the three months ended June 30, 2019 and 2018, respectively, and $509 and $0 for the six months ended June 30 2019 and 2018, respectively)	$ 88,075	$ 87,850	$ 173,657	$ 168,911
Costs and operating expenses:
Cost of revenue (exclusive of depreciation and amortization presented separately below; includes related party cost of revenue of $289 and $0 for the three months ended June 30, 2019 and 2018, respectively, and $423 and $0 for the six months ended June 30, 2019 and 2018, respectively)	8,332	7,752	17,268	15,204
Sales and marketing (includes related party expenses of $5,749 and $5,277 for the three months ended June 30, 2019 and 2018, respectively, and $11,222 and $9,818 for the six months ended June 30, 2019 and 2018, respectively)	60,233	52,014	114,971	100,432
Technology and development	16,045	15,694	31,699	31,288
General and administrative	21,382	13,494	36,486	26,975
Depreciation and amortization	6,767	5,641	13,182	10,816
Total costs and operating expenses	112,759	94,595	213,606	184,715
Loss from operations	(24,684)	(6,745)	(39,949)	(15,804)
Interest income	966	750	1,967	1,354
Interest expense	0	(662)	0	(1,323)
Loss from equity method investment	(273)	0	(273)	0
Loss before income taxes	(23,991)	(6,657)	(38,255)	(15,773)
Provision for (benefit from) income taxes	69	(35)	170	(96)
Net loss	$ (24,060)	$ (6,622)	$ (38,425)	$ (15,677)
Net loss per share attributable to common stockholders:
Net loss per share, basic and diluted (in dollars per share)	$ (0.23)	$ (0.07)	$ (0.37)	$ (0.16)
Weighted average common shares outstanding, basic and diluted (in shares)	105,485	101,150	105,139	100,862
Other comprehensive loss:
Comprehensive loss	$ (24,060)	$ (6,622)	$ (38,425)	$ (15,677)