REVENUE FROM CONTRACTS WITH CUSTOMERS - Disaggregation of Revenues by Major Business Line (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 30, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Total revenue	$ 604,569	$ 493,970
RMS
Disaggregation of Revenue [Line Items]
Total revenue	137,172	133,958
RMS | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Total revenue	54,813	48,726
RMS | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenue	82,359	85,232
DSA
Disaggregation of Revenue [Line Items]
Total revenue	354,197	259,992
DSA | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Total revenue	354,078	259,744
DSA | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenue	119	248
Manufacturing
Disaggregation of Revenue [Line Items]
Total revenue	113,200	100,020
Manufacturing | Services and products transferred over time
Disaggregation of Revenue [Line Items]
Total revenue	31,896	28,571
Manufacturing | Services and products transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenue	$ 81,304	$ 71,449