Basis of Presentation and Preparation (Details) $ in Millions	12 Months Ended
	Sep. 27, 2015 item	Sep. 28, 2014 USD ($)	Sep. 29, 2013
Principles of Consolidation and Presentation
Number of weeks in a fiscal year, low end of range	364 days
Number of weeks in a fiscal year, high end of range	371 days
Number of weeks in a fiscal year	364 days	364 days	364 days
Revenue Recognition and Contract Costs
Number of types of contracts under which revenue is recognized	3
Number of types of fixed-price contracts	2
Cash and Cash Equivalents
Maximum term of original maturity to classify instrument as cash equivalent	90 days
Restricted cash included in "Prepaid expenses and other current assets" | $		$ 4.5
Accounts Receivable - Net
Period for billing and collecting unbilled receivables	12 months
Period for earning majority of billings in excess of costs	12 months
Equipment | Maximum
Estimated useful lives
Estimated useful lives	10 years
Equipment | Minimum
Estimated useful lives
Estimated useful lives	3 years
Furniture and fixtures | Maximum
Estimated useful lives
Estimated useful lives	10 years
Furniture and fixtures | Minimum
Estimated useful lives
Estimated useful lives	3 years
Buildings | Maximum
Estimated useful lives
Estimated useful lives	40 years