Property and Equipment, net - Schedule (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross		$ 8.1	$ 3.8
Accumulated depreciation		(2.4)	(0.7)
Property and equipment, net	$ 10.8	5.7	3.1
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property and equipment, gross		4.8	1.9
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross		2.2	1.2
Furniture and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross		$ 1.1	$ 0.7

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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