Goodwill and Intangible Assets - Summary of Change in Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Goodwill
Beginning balance			$ 18,402	$ 18,402	$ 18,402
Additions to goodwill			0		0
Ending balance	$ 18,402		18,402		18,402
Intangible assets
Beginning balance			15,551	18,752	18,752
Additions to intangible assets			0		0
Amortization	(700)	$ (800)	(2,238)	$ (2,402)	(3,201)
Ending balance	$ 13,313		$ 13,313		$ 15,551

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of increase in assets, excluding financial assets, lacking physical substance with a definite life, from an acquisition.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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