CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Revenue	$ 118,327	$ 94,804	$ 345,823	$ 264,495
Costs and expenses
Cost of revenue	38,795	27,692	112,377	78,218
Sales and marketing	40,852	32,775	116,427	110,073
General and administrative	17,193	14,891	47,784	47,713
Product development	41,734	27,736	112,715	80,417
Restructuring costs	44	26,442	3,269	29,635
Amortization of purchased intangibles	488	411	1,237	1,219
Total costs and expenses	139,106	129,947	393,809	347,275
Loss from operations	(20,779)	(35,143)	(47,986)	(82,780)
Other (expense) income, net:
Interest expense, net	(9,442)	(3,159)	(27,852)	(9,161)
Other (expense) income, net	(48)	(508)	3,002	(2,484)
Total other expense, net	(9,490)	(3,667)	(24,850)	(11,645)
Loss before provision for (benefit from) income taxes	(30,269)	(38,810)	(72,836)	(94,425)
Provision for (benefit from) income taxes	2,538	(100)	2,285	(87)
Net loss	$ (32,807)	$ (38,710)	$ (75,121)	$ (94,338)
Net loss per share of common stock:
Basic net loss per common share (in dollars per share)	$ (0.47)	$ (0.58)	$ (1.09)	$ (1.44)
Diluted net loss per common share (in dollars per share)	$ (0.47)	$ (0.58)	$ (1.09)	$ (1.44)
Weighted-average shares used to compute net loss per share:
Weighted average shares outstanding used in basic net loss per common share calculation (in shares)	69,798,839	66,451,414	68,926,203	65,504,571
Weighted average shares outstanding used in diluted net loss per common share calculation (in shares)	69,798,839	66,451,414	68,926,203	65,504,571