Revenue and Contract Balances - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 27, 2020	Dec. 29, 2019	Sep. 27, 2020
Revenue from Contract with Customer [Abstract]
Contract liability revenue recognized during the period	$ 60,000	$ 64,000
Liabilities for anticipated losses	11,400		$ 13,200
Estimated cost to complete the related contracts	$ 135,000
Period for billing and collecting unbilled receivables	12 months
Unbilled accounts receivable related to claims and requests for equitable adjustment on contracts	$ 14,000		$ 14,000
Remaining unsatisfied performance obligation	$ 3,164,153
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