SEGMENT AND GEOGRAPHIC INFORMATION - Financial Information by Reportable Business Segment (Details) $ in Thousands	12 Months Ended
	Dec. 25, 2021 USD ($) segment	Dec. 26, 2020 USD ($)	Dec. 28, 2019 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment	3
Segment Reporting Information [Line Items]
Revenue	$ 3,540,160	$ 2,923,933	$ 2,621,226
Operating income	589,862	432,729	351,151
Depreciation and amortization	265,540	234,924	198,095
Capital expenditures	228,772	166,560	140,514
RMS
Segment Reporting Information [Line Items]
Revenue	690,437	571,152	537,089
Operating income	166,814	102,706	133,912
Depreciation and amortization	39,123	37,080	19,197
Capital expenditures	61,188	29,487	26,989
DSA
Segment Reporting Information [Line Items]
Revenue	2,107,231	1,837,428	1,618,995
Operating income	406,978	325,959	258,903
Depreciation and amortization	177,254	168,922	151,139
Capital expenditures	101,477	105,653	86,843
Manufacturing
Segment Reporting Information [Line Items]
Revenue	742,492	515,353	465,142
Operating income	246,390	181,494	145,420
Depreciation and amortization	46,195	25,904	23,584
Capital expenditures	$ 58,877	$ 26,287	$ 23,617