Accounts Receivable, Net - Schedule of Accounts Receivables Net (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Receivables [Abstract]
Trade accounts receivable	$ 200,584	$ 167,575
Unbilled revenue, at net realizable value	107,664	63,494
Total accounts receivable	308,248	231,069
Allowance for doubtful accounts	(14,358)	(14,894)	$ (14,379)
Accounts receivable, net	$ 293,890	$ 216,175

Amount, before allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

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- Definition

Amount, after allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

+ References

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Amount of allowance for credit loss on accounts receivable, classified as current.

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- Definition

Amounts due for billed services rendered or to be rendered, actions taken or to be taken, or a promise to refrain from taking certain actions in accordance with the terms of a legally binding agreement between the Company and, at a minimum, one other party. An example would be amounts billed to customers under contracts or programs but not paid as of the balance sheet date.

+ References

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Amount received for services rendered and products shipped, but not yet billed, for non-contractual agreements due within one year or the normal operating cycle, if longer.

+ References

No definition available.

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