Revenue from Contracts with Customers - Revenues Disaggregated by Revenue Source and Market (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2021	Sep. 23, 2020	Sep. 29, 2021	Sep. 23, 2020
Disaggregation of Revenue [Line Items]
Total revenue	$ 115,700	$ 110,979	$ 345,406	$ 315,746
Core Market
Disaggregation of Revenue [Line Items]
Total revenue	102,605	96,615	302,890	275,642
Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	13,095	14,364	42,516	40,104
Company-operated restaurant revenue
Disaggregation of Revenue [Line Items]
Total revenue	99,986	97,276	301,117	277,617
Company-operated restaurant revenue | Core Market
Disaggregation of Revenue [Line Items]
Total revenue	95,292	90,207	281,945	257,493
Company-operated restaurant revenue | Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	4,694	7,069	19,172	20,124
Franchise revenue
Disaggregation of Revenue [Line Items]
Total revenue	8,918	7,781	24,919	21,562
Franchise revenue | Core Market
Disaggregation of Revenue [Line Items]
Total revenue	4,184	3,660	11,956	10,376
Franchise revenue | Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	4,733	4,121	12,963	11,186
Franchise advertising fee revenue
Disaggregation of Revenue [Line Items]
Total revenue	6,796	5,922	19,370	16,567
Franchise advertising fee revenue | Core Market
Disaggregation of Revenue [Line Items]
Total revenue	3,129	2,748	8,989	7,773
Franchise advertising fee revenue | Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	$ 3,668	$ 3,174	$ 10,381	$ 8,794