Revenue and Contract Balances - Accounts Receivable, Net (Details) - USD ($) $ in Thousands	Dec. 27, 2020	Sep. 27, 2020
Revenue from Contract with Customer [Abstract]
Billed	$ 438,458	$ 402,818
Unbilled	242,890	253,364
Total accounts receivable	681,348	656,182
Allowance for doubtful accounts	(7,585)	(7,147)
Total accounts receivable, net	$ 673,763	$ 649,035

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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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.

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

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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.

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Unbilled amounts due for 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 entity and, at a minimum, one other party. An example would be amounts associated with contracts or programs where the recognized revenue for performance thereunder exceeds the amounts billed under the terms thereof as of the date of the balance sheet.

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