Consolidated Statements of Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenues (includes related party contra revenue of $331 and $0 for the three months ended September 30, 2019 and 2018, respectively, and $840 and $0 for the nine months ended September 30 2019 and 2018, respectively)	$ 90,555	$ 93,586	$ 264,212	$ 262,497
Costs and operating expenses:
Cost of revenue (exclusive of depreciation and amortization presented separately below; includes related party cost of revenue of $302 and $0 for the three months ended September 30, 2019 and 2018, respectively, and $725 and $0 for the nine months ended September 30, 2019 and 2018, respectively)	8,391	7,737	25,659	22,941
Sales and marketing (includes related party expenses of $6,279 and $6,514 for the three months ended September 30, 2019 and 2018, respectively, and $17,501 and $16,332 for the nine months ended September 30, 2019 and 2018, respectively)	57,961	57,031	172,932	157,463
Technology and development	13,027	15,345	44,726	46,633
General and administrative	13,018	14,030	49,504	41,005
Depreciation and amortization	6,145	5,992	19,327	16,808
Total costs and operating expenses	98,542	100,135	312,148	284,850
Loss from operations	(7,987)	(6,549)	(47,936)	(22,353)
Interest income	855	888	2,822	2,242
Interest expense	0	(662)	0	(1,985)
Loss from equity method investment	(464)	0	(737)	0
Loss before income taxes	(7,596)	(6,323)	(45,851)	(22,096)
Provision for (benefit from) income taxes	56	(72)	226	(168)
Net loss	$ (7,652)	$ (6,251)	$ (46,077)	$ (21,928)
Net loss per share attributable to common stockholders:
Net loss per share, basic and diluted (in dollars per share)	$ (0.07)	$ (0.06)	$ (0.44)	$ (0.22)
Weighted average common shares outstanding, basic and diluted (in shares)	106,239	102,765	105,510	101,503
Other comprehensive loss:
Comprehensive loss	$ (7,652)	$ (6,251)	$ (46,077)	$ (21,928)