Reportable Segments - Revenue By Client Sector (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Apr. 01, 2018	Apr. 02, 2017	Apr. 01, 2018	Apr. 02, 2017
Revenue by client sector
Threshold percentage for disclosure of revenue from a single client	10.00%	10.00%	10.00%	10.00%
Revenue	$ 700,262	$ 663,781	$ 1,460,010	$ 1,332,632
U.S. federal government
Revenue by client sector
Revenue	236,951	218,110	473,199	440,744
International
Revenue by client sector
Revenue	178,008	197,114	342,968	369,571
U.S. state and local government
Revenue by client sector
Revenue	104,905	83,181	256,659	166,676
U.S. commercial
Revenue by client sector
Revenue	$ 180,398	$ 165,376	$ 387,184	$ 355,641