Accounts Receivable - Net and Revenue Recognition (Details) (USD $)	3 Months Ended			6 Months Ended
	Mar. 29, 2015	Sep. 28, 2014	Mar. 30, 2014	Mar. 29, 2015	Mar. 30, 2014
Accounts Receivable - Net and Revenue Recognition
Billed	$ 314,993,000	$ 351,693,000		$ 314,993,000
Unbilled	359,574,000	363,050,000		359,574,000
Contract retentions	26,008,000	26,929,000		26,008,000
Total accounts receivable - gross	700,575,000	741,672,000		700,575,000
Allowance for doubtful accounts	(34,562,000)	(39,780,000)		(34,562,000)
Total accounts receivable - net	666,013,000	701,892,000		666,013,000
Billings in excess of costs on uncompleted contracts	95,270,000	103,343,000		95,270,000
Period for billing and collecting unbilled receivables				12 months
Period for earning majority of billings in excess of costs				12 months
Total accounts receivable related to claims and requests for equitable adjustment on contracts	80,000,000	79,000,000		80,000,000
Reduction in the revenue related to the evaluation of claim amounts	3,000,000
Decrease in operating income related to the evaluation of claim amounts	3,000,000
Net gains on settlement of claims			3,400,000	200,000	3,400,000
Billed accounts receivable related to U.S. federal government contracts	59,300,000	57,400,000		59,300,000
U.S. federal government unbilled receivables	68,200,000	73,200,000		68,200,000
Threshold percentage for disclosure of accounts receivable from a single client		10.00%		10.00%
Revenue Recognition and Contract Costs
Net unfavorable operating income adjustments	3,500,000		5,300,000	5,900,000	5,300,000
Liability for anticipated losses	13,600,000	18,600,000		13,600,000
Estimated cost to complete the related contracts	$ 83,900,000			$ 83,900,000
Accounts Receivable
Account receivable major customer
Number of clients exceeding threshold		0		0