Reportable Segments - Financial Information (Details)		3 Months Ended								12 Months Ended
	Jul. 01, 2019 USD ($)	Sep. 29, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jul. 01, 2018 USD ($)	Apr. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 29, 2019 USD ($) segment	Sep. 30, 2018 USD ($) segment	Oct. 01, 2017 USD ($)
Financial information concerning reportable segments
Number of renamed reportable segments | segment										2	2
Revenue										$ 3,107,348,000	$ 2,964,148,000	$ 2,753,360,000
Income from operations		$ 20,665,000	$ 64,841,000	$ 47,545,000	$ 55,711,000	$ 43,285,000	$ 55,496,000	$ 42,716,000	$ 48,589,000	188,762,000	190,086,000	183,342,000
Amortization expense for intangible assets										11,600,000	18,200,000	22,800,000
Fair value adjustments to contingent consideration liabilities										(1,085,000)	(4,252,000)	6,923,000
Total Assets		2,147,408,000				1,959,421,000				2,147,408,000	1,959,421,000
Impairment of goodwill	$ 0	7,800,000								7,755,000	0	0
GSG
Financial information concerning reportable segments
Impairment of goodwill										0
CIG
Financial information concerning reportable segments
Impairment of goodwill										7,755,000
Operating segments | GSG
Financial information concerning reportable segments
Revenue										1,820,671,000	1,694,871,000	1,487,611,000
Income from operations										185,263,000	168,211,000	138,199,000
Total Assets		587,040,000				468,010,000				587,040,000	468,010,000
Operating segments | CIG
Financial information concerning reportable segments
Revenue										1,342,509,000	1,323,142,000	1,326,020,000
Income from operations										79,633,000	74,451,000	90,817,000
Total Assets		450,276,000				478,197,000				450,276,000	478,197,000
Operating segments | RCM
Financial information concerning reportable segments
Revenue										(1,542,000)	14,199,000	18,207,000
Income from operations										(5,933,000)	(4,573,000)	(14,712,000)
Total Assets		15,608,000				25,683,000				15,608,000	25,683,000
Elimination of inter-segment revenue
Financial information concerning reportable segments
Revenue										(54,290,000)	(68,064,000)	(78,478,000)
Corporate
Financial information concerning reportable segments
Income from operations										(70,201,000)	(48,003,000)	$ (30,962,000)
Total Assets		$ 1,094,484,000				$ 987,531,000				$ 1,094,484,000	$ 987,531,000