Reportable Segments - Revenue By Sector (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 26, 2016	Jun. 28, 2015	Jun. 26, 2016	Jun. 28, 2015
Revenue by client sector
Threshold percentage for disclosure of revenue from a single client			10.00%
Revenue	$ 666,869	$ 575,108	$ 1,854,961	$ 1,720,927
International
Revenue by client sector
Revenue	194,616	124,951	537,324	445,691
U.S. commercial
Revenue by client sector
Revenue	194,089	193,098	556,635	523,839
U.S. federal government
Revenue by client sector
Revenue	203,663	186,578	546,700	541,613
U.S. state and local government
Revenue by client sector
Revenue	$ 74,501	$ 70,481	$ 214,302	$ 209,784