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SEGMENT AND GEOGRAPHIC INFORMATION - Financial Information by Reportable Business Segment (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 29, 2018 USD ($)	Sep. 29, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jul. 01, 2017 USD ($)	Apr. 01, 2017 USD ($)	Dec. 29, 2018 USD ($) segments	Dec. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting [Abstract]
Number of reportable segments \| segments									3
Segment Reporting Information [Line Items]
Revenue	$ 601,530	$ 585,295	$ 585,301	$ 493,970	$ 478,477	$ 464,232	$ 469,129	$ 445,763	$ 2,266,096	$ 1,857,601	$ 1,681,432
Operating income	$ 102,482	$ 84,362	$ 76,710	$ 67,829	$ 62,827	$ 74,062	$ 81,686	$ 69,706	331,383	288,282	237,552
Depreciation and amortization									161,779	131,159	126,658
Capital expenditures									140,054	82,431	55,288
RMS
Segment Reporting Information [Line Items]
Revenue									519,682	493,615	494,037
Operating income									136,468	114,588	136,418
Depreciation and amortization									19,469	19,627	20,853
Capital expenditures									35,172	20,879	11,642
DSA
Segment Reporting Information [Line Items]
Revenue									1,316,854	980,022	836,593
Operating income									227,577	182,796	135,379
Depreciation and amortization									112,976	79,355	71,816
Capital expenditures									73,425	36,616	27,493
Manufacturing
Segment Reporting Information [Line Items]
Revenue									429,560	383,964	350,802
Operating income									136,212	123,898	104,561
Depreciation and amortization									22,529	22,893	25,566
Capital expenditures									$ 23,323	$ 15,188	$ 12,247