REVENUE FROM CONTRACTS WITH CUSTOMERS - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 28, 2020	Dec. 28, 2019
Revenue from Contract with Customer [Abstract]
Payment terms	30 days
Unpaid advanced client billings	$ 19,000	$ 27,000
Contract liabilities (customer contract deposits)	$ 37,319	$ 33,080
Percentage of unbilled revenue billed during period	60.00%
Percentage of contract liabilities recognized as revenue during period	60.00%