BUSINESS ACQUISITIONS AND DIVESTITURE - Definite Lived Intangible Assets (Details) - USD ($) $ in Thousands	Apr. 03, 2018	Aug. 04, 2017	Sep. 28, 2016	Jun. 27, 2016	Apr. 04, 2016
MPI Research
Business Acquisition [Line Items]
Definite-Lived Intangible Assets	$ 309,200
Weighted Average Amortization Life	12 years
Brains On-Line
Business Acquisition [Line Items]
Definite-Lived Intangible Assets		$ 9,300
Weighted Average Amortization Life		12 years
Agilux
Business Acquisition [Line Items]
Definite-Lived Intangible Assets			$ 21,900
Weighted Average Amortization Life			14 years
Blue Stream
Business Acquisition [Line Items]
Definite-Lived Intangible Assets				$ 1,230
Weighted Average Amortization Life				7 years
WIL Research
Business Acquisition [Line Items]
Definite-Lived Intangible Assets					$ 164,800
Weighted Average Amortization Life					13 years
Client relationships | MPI Research
Business Acquisition [Line Items]
Definite-Lived Intangible Assets	$ 264,900
Weighted Average Amortization Life	13 years
Client relationships | Brains On-Line
Business Acquisition [Line Items]
Definite-Lived Intangible Assets		$ 7,000
Weighted Average Amortization Life		13 years
Client relationships | Agilux
Business Acquisition [Line Items]
Definite-Lived Intangible Assets			$ 16,700
Weighted Average Amortization Life			17 years
Client relationships | Blue Stream
Business Acquisition [Line Items]
Definite-Lived Intangible Assets				$ 650
Weighted Average Amortization Life				10 years
Client relationships | WIL Research
Business Acquisition [Line Items]
Definite-Lived Intangible Assets					$ 137,500
Weighted Average Amortization Life					15 years
Developed technology | MPI Research
Business Acquisition [Line Items]
Definite-Lived Intangible Assets	$ 23,400
Weighted Average Amortization Life	3 years
Developed technology | WIL Research
Business Acquisition [Line Items]
Definite-Lived Intangible Assets					$ 20,700
Weighted Average Amortization Life					3 years
Backlog | MPI Research
Business Acquisition [Line Items]
Definite-Lived Intangible Assets	$ 20,900
Weighted Average Amortization Life	1 year
Backlog | WIL Research
Business Acquisition [Line Items]
Definite-Lived Intangible Assets					$ 6,600
Weighted Average Amortization Life					1 year
Other intangible assets | Brains On-Line
Business Acquisition [Line Items]
Definite-Lived Intangible Assets		$ 2,300
Weighted Average Amortization Life		10 years
Other intangible assets | Agilux
Business Acquisition [Line Items]
Definite-Lived Intangible Assets			$ 5,200
Weighted Average Amortization Life			4 years
Other intangible assets | Blue Stream
Business Acquisition [Line Items]
Definite-Lived Intangible Assets				$ 580
Weighted Average Amortization Life				5 years