Reportable Segments - Financial Information (Details) $ in Thousands	3 Months Ended
	Dec. 27, 2020 USD ($) segment	Dec. 29, 2019 USD ($)	Sep. 27, 2020 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment	2
Revenue	$ 765,104	$ 797,623
Income from operations	66,252	63,302
Total Assets	2,414,872		$ 2,378,558
Operating segments | GSG
Segment Reporting Information [Line Items]
Revenue	468,623	457,404
Income from operations	47,700	42,048
Total Assets	659,042		649,417
Operating segments | CIG
Segment Reporting Information [Line Items]
Revenue	311,024	351,164
Income from operations	29,559	31,632
Total Assets	481,545		479,238
Operating segments | RCM
Segment Reporting Information [Line Items]
Revenue	0	145
Income from operations	0	1
Total Assets	14,256		14,258
Elimination of inter-segment revenue
Segment Reporting Information [Line Items]
Revenue	(14,543)	(11,090)
Corporate
Segment Reporting Information [Line Items]
Income from operations	(11,007)	$ (10,379)
Total Assets	$ 1,260,029		$ 1,235,645