Revenue and Contract Balances - Narrative (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 28, 2021	Mar. 29, 2020	Sep. 27, 2020
Disaggregation of Revenue [Line Items]
Contract liability revenue recognized during the period	$ 90,000	$ 105,000
Net favorable (unfavorable) operating income adjustments	1,100	$ (2,800)
Liabilities for anticipated losses	9,500		$ 13,200
Estimated cost to complete the related contracts	$ 95,000		118,000
Period for billing and collecting unbilled receivables	12 months
Unbilled accounts receivable related to claims and requests for equitable adjustment on contracts	$ 11,000		$ 11,000
Remaining unsatisfied performance obligation	$ 3,127,848
Remaining performance obligation, termination notice period one	30 days
Remaining performance obligation, termination notice period two	60 days
Remaining performance obligation, termination notice period three	90 days
CIG
Disaggregation of Revenue [Line Items]
Increase in revenue due to change in contract value	$ 2,800