REVENUE FROM CONTRACTS WITH CUSTOMERS - Disaggregation of Revenues by Major Business Line (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Disaggregation of Revenue [Line Items]
Total revenue	$ 743,300	$ 667,951	$ 2,132,943	$ 1,930,088
RMS
Disaggregation of Revenue [Line Items]
Total revenue	151,910	132,546	414,455	405,772
RMS | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Total revenue	60,225	56,243	177,623	168,377
RMS | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenue	91,685	76,303	236,832	237,395
DSA
Disaggregation of Revenue [Line Items]
Total revenue	461,177	420,079	1,342,424	1,179,793
DSA | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Total revenue	460,821	419,445	1,341,832	1,178,874
DSA | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenue	356	634	592	919
Manufacturing
Disaggregation of Revenue [Line Items]
Total revenue	130,213	115,326	376,064	344,523
Manufacturing | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Total revenue	47,457	36,308	126,088	102,674
Manufacturing | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenue	$ 82,756	$ 79,018	$ 249,976	$ 241,849