REVENUE FROM CONTRACTS WITH CUSTOMERS - Narrative (Details) $ in Thousands	6 Months Ended
	Jun. 29, 2019 USD ($)
Revenue from Contract with Customer [Abstract]
Payment terms	30 days
Unpaid advanced client billings	$ 27,000
Contract liabilities (customer contract deposits)	$ 32,923
Percentage of unbilled revenue billed during period	85.00%
Percentage of contract liabilities recognized as revenue during period	70.00%