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Stock-based Compensation - Stock-Based Compensation Costs (Details) - USD ($) $ in Thousands	3 Months Ended	4 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 4,192	$ 23,600	$ 23,625
Stock-based compensation capitalized for software development	695		695	$ 0
Total stock-based compensation cost	4,887		24,320
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	689		4,515
Product development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	1,865		3,859
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,638		$ 15,251