SEGMENT AND GEOGRAPHIC INFORMATION - Revenue by Product and Service Offering (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 28, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 29, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Segment Reporting Information [Line Items]
Revenue	$ 691,138	$ 667,951	$ 657,568	$ 604,569	$ 601,530	$ 585,295	$ 585,301	$ 493,970	$ 2,621,226	$ 2,266,096	$ 1,857,601
RMS
Segment Reporting Information [Line Items]
Revenue									537,089	519,682	493,615
DSA
Segment Reporting Information [Line Items]
Revenue									1,618,995	1,316,854	980,022
Manufacturing
Segment Reporting Information [Line Items]
Revenue									$ 465,142	$ 429,560	$ 383,964