Reportable Segments - Revenue By Sector (Details) - USD ($) $ in Thousands	3 Months Ended
	Jan. 01, 2017	Dec. 27, 2015
Revenue by client sector
Revenue	$ 668,851	$ 560,708
International
Revenue by client sector
Revenue	172,457	135,807
U.S. commercial
Revenue by client sector
Revenue	190,266	188,164
U.S. federal government
Revenue by client sector
Revenue	222,634	165,022
U.S. state and local government
Revenue by client sector
Revenue	$ 83,494	$ 71,715