Accounts Receivable and Revenue Recognition - Net Accounts Receivable and Billings in Excess of Costs on Uncompleted Contracts (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Oct. 01, 2017
Accounts Receivable - Net and Revenue Recognition
Billed	$ 464,062	$ 376,287
Unbilled	397,200	404,899
Contract retentions	13,421	39,840
Total accounts receivable – gross	874,683	821,026
Allowance for doubtful accounts	(37,580)	(32,259)
Total accounts receivable – net	837,103	788,767
Billings in excess of costs on uncompleted contracts	$ 143,270	$ 117,499

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Amounts due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer) for goods or services (including trade receivables) that have been delivered or sold in the normal course of business.

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Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

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A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

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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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Liability attributable to (i) billings in excess of costs under the percentage of completion contract accounting method representing the difference between contractually invoiced amounts (billings) and revenue recognized based, for example, on costs incurred to estimated total costs at period end or (ii) contractually invoiced amounts (billings) in excess of costs incurred and accumulated under the completed contract accounting method that are expected to be realized within one year or one operating cycle, whichever is longer, from the reporting date.

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Amount billed to customers under long-term contracts or programs that have been withheld because of retainage provisions in a contract.

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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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