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REVENUE FROM CONTRACTS WITH CUSTOMERS - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 26, 2021
Jun. 26, 2021
Jun. 27, 2020
Dec. 26, 2020
Revenue from Contract with Customer [Abstract]        
Payment terms   30 days    
Unpaid advanced client billings $ 19,000 $ 19,000   $ 16,000
Contract liabilities (customer contract deposits) 44,981 $ 44,981   $ 42,244
Percentage of unbilled revenue billed during period   80.00% 75.00%  
Amount of unbilled revenue billed during period   $ 135,000 $ 122,000  
Percentage of contract liabilities recognized as revenue during period   75.00% 75.00%  
Amount of contract liabilities recognized as revenue   $ 227,000 $ 193,000  
Lease revenue $ 6,300 $ 6,300