REVENUE FROM CONTRACTS WITH CUSTOMERS - Disaggregation of Revenues by Major Business Line (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 27, 2021	Mar. 28, 2020
Disaggregation of Revenue [Line Items]
Total revenue	$ 824,566	$ 707,059
RMS
Disaggregation of Revenue [Line Items]
Total revenue	176,910	145,996
RMS | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Total revenue	64,896	60,041
RMS | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenue	112,014	85,955
DSA
Disaggregation of Revenue [Line Items]
Total revenue	501,178	438,683
DSA | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Total revenue	500,468	438,564
DSA | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenue	710	119
Manufacturing
Disaggregation of Revenue [Line Items]
Total revenue	146,478	122,380
Manufacturing | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Total revenue	50,568	37,314
Manufacturing | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenue	$ 95,910	$ 85,066