Reportable Segments (Details 3) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 27, 2015 USD ($)	Jun. 28, 2015 USD ($)	Mar. 29, 2015 USD ($)	Dec. 28, 2014 USD ($)	Sep. 28, 2014 USD ($)	Jun. 29, 2014 USD ($)	Mar. 30, 2014 USD ($)	Dec. 29, 2013 USD ($)	Sep. 27, 2015 USD ($) item	Sep. 28, 2014 USD ($) item	Sep. 29, 2013 USD ($) item
Revenue by client sector
Threshold percentage for disclosure of revenue from a single client									10.00%	10.00%	10.00%
Revenue	$ 578,394	$ 575,108	$ 564,763	$ 581,056	$ 622,179	$ 629,502	$ 586,285	$ 645,848	$ 2,299,321	$ 2,483,814	$ 2,613,755
International
Revenue by client sector
Revenue									564,882	643,649	697,975
U.S. commercial
Revenue by client sector
Revenue									736,815	713,266	693,677
U.S. federal government
Revenue by client sector
Revenue									709,600	772,290	829,790
U.S. state and local government
Revenue by client sector
Revenue									$ 288,024	$ 354,609	$ 392,313
Accounts Receivable
Revenue by client sector
Number of clients exceeding threshold | item									0	0	0