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REVENUE - Liability Balance (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 23, 2020
Sep. 25, 2019
Sep. 23, 2020
Sep. 25, 2019
Revenue from Contract with Customer [Abstract]        
Gift card liability $ 91 $ 84 $ 436 $ 467
Deferred revenue $ 234 $ 86 $ 539 $ 305