Reportable Segments - Financial Information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 27, 2021 USD ($)	Jun. 28, 2020 USD ($)	Jun. 27, 2021 USD ($) segment	Jun. 28, 2020 USD ($)	Sep. 27, 2020 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			2
Revenue	$ 801,633	$ 709,771	$ 2,321,500	$ 2,241,527
Income from operations	69,807	63,525	196,865	174,356
Total Assets	2,510,921		2,510,921		$ 2,378,558
Operating segments | GSG
Segment Reporting Information [Line Items]
Revenue	488,700	432,180	1,431,151	1,326,487
Income from operations	49,297	43,100	143,106	120,495
Total Assets	642,830		642,830		649,417
Operating segments | CIG
Segment Reporting Information [Line Items]
Revenue	327,434	291,021	931,586	950,597
Income from operations	34,017	28,848	89,886	82,156
Total Assets	470,009		470,009		479,238
Operating segments | RCM
Segment Reporting Information [Line Items]
Revenue	143	48	613	198
Income from operations	0	(1)	1	0
Total Assets	11,760		11,760		14,258
Elimination of inter-segment revenue
Segment Reporting Information [Line Items]
Revenue	(14,644)	(13,478)	(41,850)	(35,755)
Corporate
Segment Reporting Information [Line Items]
Income from operations	(13,507)	$ (8,422)	(36,128)	$ (28,295)
Total Assets	$ 1,386,322		$ 1,386,322		$ 1,235,645