REVENUE FROM CONTRACTS WITH CUSTOMERS - Disaggregation of Revenues by Major Business Line (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 25, 2021	Dec. 26, 2020	Dec. 28, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 3,540,160	$ 2,923,933	$ 2,621,226
RMS
Disaggregation of Revenue [Line Items]
Revenue	690,437	571,152	537,089
RMS | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Revenue	263,659	240,480	227,872
RMS | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	426,778	330,672	309,217
DSA
Disaggregation of Revenue [Line Items]
Revenue	2,107,231	1,837,428	1,618,995
DSA | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Revenue	2,103,415	1,836,519	1,618,281
DSA | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	3,816	909	714
Manufacturing
Disaggregation of Revenue [Line Items]
Revenue	742,492	515,353	465,142
Manufacturing | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Revenue	335,745	174,254	142,896
Manufacturing | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenue	$ 406,747	$ 341,099	$ 322,246