REVENUE FROM CONTRACTS WITH CUSTOMERS - Disaggregation of Revenues by Major Business Line (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 25, 2021	Sep. 26, 2020	Sep. 25, 2021	Sep. 26, 2020
Disaggregation of Revenue [Line Items]
Total revenue	$ 895,937	$ 743,300	$ 2,635,110	$ 2,132,943
RMS
Disaggregation of Revenue [Line Items]
Total revenue	171,258	151,910	524,862	414,455
RMS | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Total revenue	65,805	60,225	197,035	177,623
RMS | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenue	105,453	91,685	327,827	236,832
DSA
Disaggregation of Revenue [Line Items]
Total revenue	531,823	461,177	1,573,095	1,342,424
DSA | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Total revenue	531,637	460,821	1,571,895	1,341,832
DSA | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenue	186	356	1,200	592
Manufacturing
Disaggregation of Revenue [Line Items]
Total revenue	192,856	130,213	537,153	376,064
Manufacturing | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Total revenue	93,473	47,457	240,015	126,088
Manufacturing | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenue	$ 99,383	$ 82,756	$ 297,138	$ 249,976