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REVENUE RECOGNITION - Percentage of completion (Details) - USD ($)
$ in Thousands
Sep. 26, 2020
Dec. 28, 2019
Sep. 28, 2019
REVENUE RECOGNITION      
Cost and Earnings in Excess of Billings $ 4,130 $ 4,690 $ 6,815
Billings in Excess of Cost and Earnings $ 11,264 $ 6,622 $ 6,666