CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Revenue	$ 119,605	$ 91,603	$ 227,496	$ 169,691
Costs and expenses
Cost of revenue	40,063	27,707	73,582	50,526
Sales and marketing	38,622	34,618	75,575	77,298
General and administrative	16,105	16,353	30,591	32,822
Product development	37,526	26,967	70,981	52,681
Restructuring costs	493	0	3,225	3,193
Amortization of purchased intangibles	374	404	749	809
Total costs and expenses	133,183	106,049	254,703	217,329
Loss from operations	(13,578)	(14,446)	(27,207)	(47,638)
Other (expense) income, net:
Interest expense, net	(9,281)	(3,211)	(18,410)	(6,002)
Other income (expense), net	2,338	(1,309)	3,050	(1,975)
Total other (expense) income, net	(6,943)	(4,520)	(15,360)	(7,977)
Loss before provision for (benefit from) income taxes	(20,521)	(18,966)	(42,567)	(55,615)
Provision for (benefit from) income taxes	598	(339)	(253)	13
Net loss	$ (21,119)	$ (18,627)	$ (42,314)	$ (55,628)
Net loss per share of common stock:
Basic net loss per common share (in dollars per share)	$ (0.31)	$ (0.28)	$ (0.62)	$ (0.86)
Diluted net loss per common share (in dollars per share)	$ (0.31)	$ (0.28)	$ (0.62)	$ (0.86)
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)	69,057,129	65,650,782	68,482,653	65,023,302
Weighted average shares outstanding used in diluted net loss per common share calculation (in shares)	69,057,129	65,650,782	68,482,653	65,023,302