BUSINESS ACQUISITIONS AND DIVESTITURE - Additional Information (Details) € in Millions, £ in Millions							3 Months Ended		9 Months Ended		12 Months Ended
	Apr. 03, 2018 USD ($)	Jan. 11, 2018 USD ($)	Aug. 04, 2017 USD ($)	Sep. 28, 2016 USD ($)	Jun. 27, 2016 USD ($)	Apr. 04, 2016 USD ($)	Sep. 30, 2017 USD ($)	Apr. 01, 2017 USD ($)	Dec. 29, 2018 USD ($)	Dec. 31, 2016 USD ($)	Dec. 29, 2018 USD ($)	Dec. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 29, 2018 USD ($)	Sep. 29, 2018 GBP (£)	Mar. 26, 2018 USD ($)	Jan. 11, 2018 GBP (£)	Aug. 04, 2017 EUR (€)	Aug. 04, 2017 USD ($)	Feb. 10, 2017 USD ($)	Mar. 30, 2016 USD ($)
Business Acquisition [Line Items]
Amount of credit facility																					$ 1,650,000,000.00
Gain on divestiture											$ 0	$ 10,577,000	$ 0
CDMO Business | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Business Acquisition [Line Items]
Cash received from divestiture																				$ 75,000,000
Cash and cash equivalents transferred																				600,000
Working capital adjustments																				300,000
Gain on divestiture								$ 10,600,000
Credit facility | $2.3 Billion Credit Facility
Business Acquisition [Line Items]
Amount of credit facility																$ 2,300,000,000.0
MPI Research
Business Acquisition [Line Items]
Purchase price	$ 829,700,000
Purchase price allocation	800,800,000
Cash acquired	27,700,000
Adjustments to purchase price	1,200,000
Goodwill resulting from transaction	$ 4,100,000
Transaction and integration costs											16,500,000
Revenue since acquisition									$ 209,500,000
Operating income (loss) since acquisition									$ 33,400,000
Weighted average life	12 years
MPI Research | Client relationships
Business Acquisition [Line Items]
Weighted average life	13 years
MPI Research | Depreciation and Amortization Expense
Business Acquisition [Line Items]
Adjustments to purchase price											14,100,000	22,400,000
MPI Research | Interest expense
Business Acquisition [Line Items]
Adjustments to purchase price											2,800,000	27,100,000
KWS BioTest Limited
Business Acquisition [Line Items]
Purchase price		$ 20,300,000
Purchase price allocation		21,529,000
Cash acquired		1,000,000
Adjustments to purchase price		400,000
Transaction and integration costs											$ 700,000
Contingent consideration		$ 3,800,000												$ 2,500,000	£ 2.0		£ 3.0
KWS BioTest Limited | Client relationships
Business Acquisition [Line Items]
Weighted average life											12 years
Brains On-Line
Business Acquisition [Line Items]
Purchase price			$ 21,300,000
Purchase price allocation																			$ 20,122,000
Cash acquired			$ 600,000
Transaction and integration costs											$ 0	2,600,000
Contingent consideration																		€ 6.7	$ 7,700,000
Weighted average life			12 years
Brains On-Line | Client relationships
Business Acquisition [Line Items]
Weighted average life			13 years
Agilux
Business Acquisition [Line Items]
Purchase price				$ 64,900,000
Purchase price allocation				62,025,000
Cash acquired				$ 2,900,000
Transaction and integration costs											0	300,000	1,700,000
Weighted average life				14 years
Agilux | Client relationships
Business Acquisition [Line Items]
Weighted average life				17 years
Blue Stream
Business Acquisition [Line Items]
Purchase price					$ 11,700,000
Purchase price allocation					$ 11,749,000
Transaction and integration costs											0	0	600,000
Weighted average life					7 years
Contingent consideration payable					$ 3,000,000
Contingent consideration paid							$ 3,000,000
Blue Stream | Client relationships
Business Acquisition [Line Items]
Weighted average life					10 years
WIL Research
Business Acquisition [Line Items]
Purchase price						$ 604,800,000
Purchase price allocation						577,391,000
Cash acquired						27,400,000
Goodwill resulting from transaction						$ 19,000,000														$ 14,800,000
Transaction and integration costs											$ 0	$ 1,700,000	15,500,000
Revenue since acquisition										$ 176,100,000
Operating income (loss) since acquisition										$ 12,500,000
Weighted average life						13 years
Assumed liabilities						$ 400,000
Additional amortization of intangible assets and depreciation of fixed assets													400,000
Reversal of interest expense on borrowings													$ 2,600,000
WIL Research | Client relationships
Business Acquisition [Line Items]
Weighted average life						15 years