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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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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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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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services 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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Property and Equipment, net (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	$ 66,124		$ 63,369	$ 67,884
Less: Accumulated depreciation	(43,249)		(37,824)	(38,341)
Property and equipment, net	22,875		25,545	29,543
Depreciation	5,600	$ 6,200	8,100	8,700	$ 9,200
Leasehold improvements
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	50,528		49,074	46,865
Furniture and fixtures
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	8,281		8,027	7,470
Computer equipment
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	6,602		5,625	12,950
Video equipment
Property, Plant and Equipment, Net, by Type [Abstract]
Property and equipment, gross	$ 713		$ 643	$ 599