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Contracts with Customers - Summary of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 29, 2017
Disaggregation Of Revenue [Line Items]
Revenues	$ 1,037,388	$ 1,023,277	$ 989,742	$ 904,405	$ 928,940	$ 976,157	$ 900,732	$ 754,679	$ 3,954,812	$ 3,560,508	$ 3,017,011
Cost-Plus
Disaggregation Of Revenue [Line Items]
Revenues									1,705,832	1,473,815
Time-and-Materials
Disaggregation Of Revenue [Line Items]
Revenues									1,074,037	961,759
Fixed-Price
Disaggregation Of Revenue [Line Items]
Revenues									$ 1,174,943	$ 1,124,934

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

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