CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue	$ 91,603,000	$ 70,959,000	$ 169,691,000	$ 137,361,000
Costs and expenses
Cost of revenue	27,707,000	18,049,000	50,526,000	36,698,000
Sales and marketing	34,618,000	39,343,000	77,298,000	72,379,000
General and administrative	16,353,000	13,763,000	32,822,000	27,930,000
Product development	26,967,000	20,182,000	52,681,000	38,355,000
Restructuring costs	0	205,000	3,193,000	484,000
Amortization of purchased intangibles	404,000	438,000	809,000	899,000
Total costs and expenses	106,049,000	91,980,000	217,329,000	176,745,000
Loss from operations	(14,446,000)	(21,021,000)	(47,638,000)	(39,384,000)
Other (expense) income, net
Interest expense, net	(3,211,000)	(2,017,000)	(6,002,000)	(2,684,000)
Other (expense) income, net	(1,309,000)	(250,000)	(1,975,000)	483,000
Total other (expense) income, net	(4,520,000)	(2,267,000)	(7,977,000)	(2,201,000)
Loss before provision for income taxes	(18,966,000)	(23,288,000)	(55,615,000)	(41,585,000)
(Benefit from) provision for income taxes	(339,000)	699,000	13,000	1,292,000
Net loss	$ (18,627,000)	$ (23,987,000)	$ (55,628,000)	$ (42,877,000)
Net loss per share of common stock:
Basic net loss per common share (in dollars per share)	$ (0.28)	$ (0.38)	$ (0.86)	$ (0.69)
Diluted net loss per common share (in dollars per share)	$ (0.28)	$ (0.38)	$ (0.86)	$ (0.69)
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)	65,650,782	62,350,787	65,023,302	61,899,072
Weighted average shares outstanding used in diluted net loss per common share calculation (in shares)	65,650,782	62,350,787	65,023,302	61,899,072
Cost of revenue
Additional Information on Operating Expenses
Stock-based compensation expense	$ 2,199,000	$ 528,000	$ 3,448,000	$ 1,148,000
Depreciation expense	2,537,000	1,954,000	4,909,000	3,981,000
Amortization of purchased intangibles	284,000	285,000	569,000	570,000
Sales and marketing
Additional Information on Operating Expenses
Stock-based compensation expense	2,525,000	2,095,000	7,664,000	3,694,000
Depreciation expense	620,000	429,000	1,287,000	786,000
General and administrative
Additional Information on Operating Expenses
Stock-based compensation expense	4,083,000	2,825,000	6,811,000	5,391,000
Depreciation expense	49,000	225,000	154,000	456,000
Product development
Additional Information on Operating Expenses
Stock-based compensation expense	7,138,000	3,857,000	12,719,000	6,238,000
Depreciation expense	$ 2,532,000	$ 1,154,000	$ 4,924,000	$ 2,420,000