REVENUE FROM CONTRACTS WITH CUSTOMERS - Revenues Disaggregated by Revenue Source and Market (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2023	Sep. 28, 2022	Sep. 27, 2023	Sep. 28, 2022
Disaggregation of Revenue [Line Items]
Total revenue	$ 120,399	$ 119,878	$ 356,417	$ 354,037
Core Market
Disaggregation of Revenue [Line Items]
Total revenue	106,443	106,569	314,086	313,365
Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	13,956	13,309	42,331	40,672
Company-operated restaurant revenue
Disaggregation of Revenue [Line Items]
Total revenue	102,703	103,174	304,477	303,585
Company-operated restaurant revenue | Core Market
Disaggregation of Revenue [Line Items]
Total revenue	97,966	98,732	289,534	289,798
Company-operated restaurant revenue | Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	4,737	4,442	14,943	13,787
Franchise revenue
Disaggregation of Revenue [Line Items]
Total revenue	10,255	9,543	30,046	28,862
Franchise revenue | Core Market
Disaggregation of Revenue [Line Items]
Total revenue	5,021	4,501	14,454	13,559
Franchise revenue | Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	5,234	5,042	15,592	15,303
Franchise advertising fee revenue
Disaggregation of Revenue [Line Items]
Total revenue	7,441	7,161	21,894	21,590
Franchise advertising fee revenue | Core Market
Disaggregation of Revenue [Line Items]
Total revenue	3,456	3,336	10,098	10,008
Franchise advertising fee revenue | Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	$ 3,985	$ 3,825	$ 11,796	$ 11,582