Property and equipment, net - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 301,253	$ 294,881
Less: Accumulated depreciation	(208,952)	(181,783)
Total property and equipment, net	92,301	113,098
Computer software and web development [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	253,296	231,943
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	23,449	23,691
Building [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	5,158	5,158
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	4,600	5,157
Furniture, fixtures and equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	1,874	2,442
Computer Software and Web Development Projects In-process [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 12,876	$ 26,490