Restatement of Previously Issued Consolidated Financial Statements - Consolidated statement of operations (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Restatement of Previously Issued Consolidated Financial Statements
Revenue	$ 72,299	$ 77,595
Operating expenses:
Selling and marketing	41,665	56,220
Product and technology	28,546	30,992
General and administrative	28,199	52,011
Total operating expenses	114,530	165,717
Operating loss	(42,231)	(88,122)
Other income (expense):
Other income (expense), net	1,244	(7,967)
Total other income (expense)	(13,490)	(15,101)
Loss before income taxes	(55,721)	(103,223)
Income tax (benefit) expense	(1,689)	96
Net loss	(54,032)	(103,319)
Net loss attributable to common stockholders	$ (71,316)	$ (103,319)
Net loss attributable per share to common stockholders:
Basic	$ (1.96)	$ (3.31)
Diluted	$ (2.03)	$ (3.31)
As Filed
Restatement of Previously Issued Consolidated Financial Statements
Revenue	$ 73,216
Operating expenses:
Selling and marketing	41,768
Product and technology	28,298
General and administrative	28,387
Total operating expenses	114,573
Operating loss	(41,357)
Other income (expense):
Other income (expense), net	2,791
Total other income (expense)	(11,943)
Loss before income taxes	(53,300)
Income tax (benefit) expense	(1,691)
Net loss	(51,609)
Net loss attributable to common stockholders	$ (68,893)
Net loss attributable per share to common stockholders:
Basic	$ (1.90)
Diluted	$ (1.90)
Restatement Adjustments
Restatement of Previously Issued Consolidated Financial Statements
Revenue	$ (917)
Operating expenses:
Selling and marketing	(103)
Product and technology	248
General and administrative	(188)
Total operating expenses	(43)
Operating loss	(874)
Other income (expense):
Other income (expense), net	(1,547)
Total other income (expense)	(1,547)
Loss before income taxes	(2,421)
Income tax (benefit) expense	2
Net loss	(2,423)
Net loss attributable to common stockholders	$ (2,423)
Net loss attributable per share to common stockholders:
Basic	$ (0.06)
Diluted	$ (0.13)
Restatement Adjustments | Other immaterial items
Other income (expense):
Net loss	$ 900