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REVENUE FROM CONTRACTS WITH CUSTOMERS - Narrative (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 30, 2019
Dec. 29, 2018
Revenue from Contract with Customer [Abstract]    
Payment terms 30 days  
Unpaid advanced client billings $ 12,000  
Contract liabilities (customer contract deposits) $ 32,380 $ 38,245
Percentage of unbilled revenue billed during period 70.00%  
Percentage of contract liabilities recognized as revenue during period 60.00%