Reportable Segments - Financial Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Apr. 01, 2018 USD ($)	Apr. 02, 2017 USD ($)	Apr. 01, 2018 USD ($) segment	Apr. 02, 2017 USD ($)	Oct. 01, 2017 USD ($)
Financial information regarding reportable segments
Number of renamed reportable segments | segment			2
Revenue	$ 700,262	$ 663,781	$ 1,460,010	$ 1,332,632
Income (loss) from operations	42,716	42,956	91,305	82,811
Total Assets	2,082,793		2,082,793		$ 1,902,745
Operating segment | GSG
Financial information regarding reportable segments
Revenue	406,027	357,113	848,799	719,973
Income (loss) from operations	34,177	33,432	73,302	63,600
Total Assets	488,073		488,073		378,839
Operating segment | CIG
Financial information regarding reportable segments
Revenue	309,704	329,127	641,217	647,198
Income (loss) from operations	18,400	18,459	39,693	40,003
Total Assets	507,493		507,493		518,697
Operating segment | RCM
Financial information regarding reportable segments
Revenue	1,480	(23)	8,286	8,209
Income (loss) from operations	(489)	(8,466)	(1,647)	(11,508)
Total Assets	31,092		31,092		33,620
Elimination of inter-segment revenue
Financial information regarding reportable segments
Revenue	(16,949)	(22,436)	(38,292)	(42,748)
Corporate
Financial information regarding reportable segments
Income (loss) from operations	(9,372)	$ (469)	(20,043)	$ (9,284)
Total Assets	$ 1,056,135		$ 1,056,135		$ 971,589