Accounts Receivable - Net and Revenue Recognition (Details) $ in Thousands	12 Months Ended
	Sep. 27, 2015 USD ($) claim item	Sep. 28, 2014 USD ($) item	Sep. 29, 2013 item
Billed	$ 331,364	$ 351,693
Unbilled	311,823	363,050
Contract retentions	24,333	26,929
Total accounts receivable - gross	667,520	741,672
Allowance for doubtful accounts	(31,490)	(39,780)
Total accounts receivable - net	636,030	701,892
Billings in excess of costs on uncompleted contracts	$ 93,989	103,343
Period for billing and collecting unbilled receivables	12 months
Period for earning majority of billings in excess of costs	12 months
Unbilled accounts receivable related to claims and requests for equitable adjustment on contracts	$ 53,000	79,000
Number of claims settled | claim	2
Claims settlement amount	$ 31,000
Cash proceeds from claim settlement	29,000
Reduction in the revenue related to the evaluation of claim amounts	2,000
Decrease in operating income related to the evaluation of claim amounts	2,000
Loss on uncollectible accounts receivable related to claims	1,800
Revenue recognized related to the evaluation of claim amounts		3,400
Increase in operating income related to the evaluation of claim amounts		3,400
Billed accounts receivable related to U.S. federal government contracts	61,900	57,400
U.S. federal government unbilled receivables	$ 74,200	$ 73,200
Threshold percentage for disclosure of accounts receivable from a single client	10.00%	10.00%
Accounts Receivable
Number of clients exceeding threshold | item	0	0	0