Consolidated Statements of Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Revenues (includes related party contra revenue of $1,189, $0, and $0, for the years ended December 31, 2019, 2018, and 2017, respectively)	$ 353,880	$ 353,571	$ 323,149
Costs and operating expenses:
Cost of revenue (exclusive of depreciation and amortization presented separately below and includes related party expenses of $966, $0, and $0, for the years ended December 31, 2019, 2018, and 2017, respectively)	33,427	31,154	28,227
Sales and marketing (includes related party expenses of $23,191, $22,128, and $16,531, for the years ended December 31, 2019, 2018, and 2017, respectively)	229,342	213,415	185,397
Technology and development	57,188	61,348	59,070
General and administrative	65,148	54,140	61,646
Depreciation and amortization	25,591	22,677	22,472
Total costs and operating expenses	410,696	382,734	356,812
Loss from operations	(56,816)	(29,163)	(33,663)
Interest income	3,495	3,314	1,260
Interest expense	0	(2,649)	(2,610)
Loss before income taxes	(54,601)	(28,498)	(35,013)
Provision for / (benefit from) income taxes	289	(177)	(2,164)
Net loss	$ (54,890)	$ (28,321)	$ (32,849)
Net loss per share, basic and diluted (in dollars per share)	$ (0.52)	$ (0.28)	$ (0.35)
Weighted average common shares outstanding, basic and diluted	105,805	102,149	94,865
Other comprehensive loss:
Comprehensive loss	$ (54,890)	$ (28,321)	$ (32,849)
Income (Loss) from Equity Method Investments	$ (1,280)	$ 0	$ 0