Business Acquisitions - Summary of the fair values of assets acquired and liabilities assumed (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 28, 2019	Dec. 29, 2018
Finite-Lived Intangible Assets [Line Items]
Cash	$ 6,969	$ 345
Billed and unbilled receivables, net	64,165	20,999
Right-of-use assets	6,131	0
Property and equipment	15,789	3,122
Prepaid expenses	3,609	589
Other assets	2,365	83
Total Assets	276,027	72,197
Liabilities	(32,022)	(11,589)
Deferred tax liabilities	(43,151)	(8,903)
Net assets acquired	200,854	51,705
Consideration paid (Cash, Notes and/or stock)	368,950	90,516
Contingent consideration (earn-out)	1,004	3,112
Total Consideration	369,954	93,628
Excess consideration over the amounts assigned to the net assets acquired (Goodwill)	169,100	41,923
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets	75,132	32,267
Trade name
Finite-Lived Intangible Assets [Line Items]
Intangible assets	59,911	2,479
Customer backlog
Finite-Lived Intangible Assets [Line Items]
Intangible assets	8,198	8,007
Developed technology
Finite-Lived Intangible Assets [Line Items]
Intangible assets	32,944	0
Other
Finite-Lived Intangible Assets [Line Items]
Intangible assets	814	$ 4,306
QSI
Finite-Lived Intangible Assets [Line Items]
Cash	6,894
Billed and unbilled receivables, net	42,523
Right-of-use assets	6,131
Property and equipment	13,626
Prepaid expenses	2,612
Other assets	1,317
Total Assets	236,137
Liabilities	(23,698)
Deferred tax liabilities	(39,372)
Net assets acquired	173,067
Consideration paid (Cash, Notes and/or stock)	318,004
Contingent consideration (earn-out)	0
Total Consideration	318,004
Excess consideration over the amounts assigned to the net assets acquired (Goodwill)	144,937
QSI | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets	64,709
QSI | Trade name
Finite-Lived Intangible Assets [Line Items]
Intangible assets	58,546
QSI | Customer backlog
Finite-Lived Intangible Assets [Line Items]
Intangible assets	6,835
QSI | Developed technology
Finite-Lived Intangible Assets [Line Items]
Intangible assets	32,944
QSI | Other
Finite-Lived Intangible Assets [Line Items]
Intangible assets	0
Other
Finite-Lived Intangible Assets [Line Items]
Cash	75
Billed and unbilled receivables, net	21,642
Right-of-use assets	0
Property and equipment	2,163
Prepaid expenses	997
Other assets	1,048
Total Assets	39,890
Liabilities	(8,324)
Deferred tax liabilities	(3,779)
Net assets acquired	27,787
Consideration paid (Cash, Notes and/or stock)	50,946
Contingent consideration (earn-out)	1,004
Total Consideration	51,950
Excess consideration over the amounts assigned to the net assets acquired (Goodwill)	24,163
Other | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Intangible assets	10,423
Other | Trade name
Finite-Lived Intangible Assets [Line Items]
Intangible assets	1,365
Other | Customer backlog
Finite-Lived Intangible Assets [Line Items]
Intangible assets	1,363
Other | Developed technology
Finite-Lived Intangible Assets [Line Items]
Intangible assets	0
Other | Other
Finite-Lived Intangible Assets [Line Items]
Intangible assets	$ 814