REVENUE FROM CONTRACTS WITH CUSTOMERS - Disaggregation of Revenues by Major Business Line (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 26, 2021	Jun. 27, 2020	Jun. 26, 2021	Jun. 27, 2020
Disaggregation of Revenue [Line Items]
Total revenue	$ 914,607	$ 682,584	$ 1,739,173	$ 1,389,643
RMS
Disaggregation of Revenue [Line Items]
Total revenue	176,694	116,549	353,604	262,545
RMS | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Total revenue	66,334	57,357	131,230	117,398
RMS | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenue	110,360	59,192	222,374	145,147
DSA
Disaggregation of Revenue [Line Items]
Total revenue	540,094	442,564	1,041,272	881,247
DSA | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Total revenue	539,790	442,447	1,040,258	881,011
DSA | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenue	304	117	1,014	236
Manufacturing
Disaggregation of Revenue [Line Items]
Total revenue	197,819	123,471	344,297	245,851
Manufacturing | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Total revenue	95,974	41,317	146,542	78,631
Manufacturing | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenue	$ 101,845	$ 82,154	$ 197,755	$ 167,220