Summary of Significant Accounting Policies - Internally Developed Software Costs (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Property, Plant and Equipment [Line Items]
Capitalized internally developed software costs	$ 4,135	$ 3,555	$ 12,436	$ 10,938
Amortization of internally developed software costs	$ 5,686	$ 2,091	$ 12,433	$ 5,373
Capitalized Computer Software
Property, Plant and Equipment [Line Items]
Amortization period			3 years

Additions made to capitalized computer software costs during the period.

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-Topic 350
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Amount of expense for amortization of capitalized computer software costs.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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