Reportable Segments - Revenue By Client Sector (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Apr. 02, 2017	Mar. 27, 2016	Apr. 02, 2017	Mar. 27, 2016
Revenue by client sector
Revenue	$ 663,781	$ 627,384	$ 1,332,632	$ 1,188,092
U.S. federal government
Revenue by client sector
Revenue	218,110	178,015	440,744	343,037
International
Revenue by client sector
Revenue	197,114	206,902	369,571	342,708
U.S. state and local government
Revenue by client sector
Revenue	83,181	68,086	166,676	139,802
U.S. commercial
Revenue by client sector
Revenue	$ 165,376	$ 174,381	$ 355,641	$ 362,545