REVENUE FROM CONTRACTS WITH CUSTOMERS - Disaggregation of Revenues by Major Business Line (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 28, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 29, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue	$ 691,138	$ 667,951	$ 657,568	$ 604,569	$ 601,530	$ 585,295	$ 585,301	$ 493,970	$ 2,621,226	$ 2,266,096	$ 1,857,601
RMS
Disaggregation of Revenue [Line Items]
Revenue									537,089	519,682	493,615
RMS | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Revenue									227,872	202,872
RMS | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue									309,217	316,810
DSA
Disaggregation of Revenue [Line Items]
Revenue									1,618,995	1,316,854	980,022
DSA | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Revenue									1,618,281	1,316,005
DSA | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue									714	849
Manufacturing
Disaggregation of Revenue [Line Items]
Revenue									465,142	429,560	$ 383,964
Manufacturing | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Revenue									142,896	128,287
Manufacturing | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue									$ 322,246	$ 301,273