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Income Taxes (Reconciliation of Unrecognized Tax Benefits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 28, 2018	Sep. 29, 2017	Sep. 30, 2016
Reconciliation Of Unrecognized Tax Benefits Excluding Amounts Pertaining To Examined Tax Returns Roll Forward [Abstract]
Balance, beginning of year	$ 38,580	$ 44,167	$ 42,666
Acquisition of CH2M	137,912	0	0
Additions based on tax positions related to the current year	9,780	5,900	5,670
Additions for tax positions of prior years	5,561	237	367
Reductions for tax positions of prior years	(8,962)	(4,524)	(2,451)
Settlement	(3,731)	(7,200)	(2,085)
Balance, end of year	$ 179,140	$ 38,580	$ 44,167

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- Definition

Reconciliation Of Unrecognized Tax Benefits Excluding Amounts Pertaining To Examined Tax Returns Roll Forward [Abstract]

+ References

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Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319

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-Section 50
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