SEGMENT INFORMATION - Revenue and Other Financial Information by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 27, 2021	Mar. 28, 2020
Segment Reporting Information [Line Items]
Revenue	$ 824,566	$ 707,059
Operating income	123,703	94,281
Depreciation and amortization	61,508	57,260
Capital expenditures	28,030	25,721
RMS
Segment Reporting Information [Line Items]
Revenue	176,910	145,996
Operating income	44,935	27,373
Depreciation and amortization	9,679	8,752
Capital expenditures	2,983	5,412
DSA
Segment Reporting Information [Line Items]
Revenue	501,178	438,683
Operating income	90,949	72,283
Depreciation and amortization	44,608	41,330
Capital expenditures	17,040	14,729
Manufacturing
Segment Reporting Information [Line Items]
Revenue	146,478	122,380
Operating income	49,437	41,112
Depreciation and amortization	6,569	6,366
Capital expenditures	$ 7,110	$ 5,161