Reportable Segments - Financial Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Jul. 01, 2018 USD ($)	Jul. 02, 2017 USD ($)	Jul. 01, 2018 USD ($) segment	Jul. 02, 2017 USD ($)	Oct. 01, 2017 USD ($)
Financial information regarding reportable segments
Number of renamed reportable segments | segment			2
Revenue	$ 764,795	$ 685,539	$ 2,224,805	$ 2,018,171
Income (loss) from operations	55,496	45,884	146,801	128,695
Total Assets	2,033,830		2,033,830		$ 1,902,745
Operating segment | GSG
Financial information regarding reportable segments
Revenue	423,912	379,292	1,272,712	1,099,265
Income (loss) from operations	44,372	32,047	117,674	95,647
Total Assets	483,327		483,327		378,839
Operating segment | CIG
Financial information regarding reportable segments
Revenue	352,631	318,195	993,849	965,393
Income (loss) from operations	27,892	24,082	67,585	64,085
Total Assets	485,595		485,595		518,697
Operating segment | RCM
Financial information regarding reportable segments
Revenue	3,336	4,192	11,622	12,401
Income (loss) from operations	(485)	(1,251)	(2,132)	(12,759)
Total Assets	26,938		26,938		33,620
Elimination of inter-segment revenue
Financial information regarding reportable segments
Revenue	(15,084)	(16,140)	(53,378)	(58,888)
Corporate
Financial information regarding reportable segments
Income (loss) from operations	(16,283)	$ (8,994)	(36,326)	$ (18,278)
Total Assets	$ 1,037,970		$ 1,037,970		$ 971,589