LEASES - Maturities of lease liabilities (Details) - USD ($) $ in Thousands	Apr. 03, 2020	Dec. 27, 2019
Operating
Remainder of 2020	$ 6,651
2021	5,646
2022	4,882
2023	3,035
2024	2,296
2025 and thereafter	4,019
Total lease payments	26,529
Less: Imputed interest	(2,761)
Total lease obligations	23,768	$ 23,961
Less: Current obligations	5,717	5,550
Noncurrent lease obligations	18,051	18,411
Finance
Remainder of 2020	441
2021	181
2022	58
2023	5
2024	4
Total lease payments	689
Less: Imputed interest	(26)
Total lease obligations	663	566
Finance lease obligations	421	375
Finance lease obligations, less current portion	$ 242	$ 191