Revenue from Contracts with Customers - Revenues Disaggregated by Revenue Source and Market (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 25, 2019	Sep. 26, 2018	Sep. 25, 2019	Sep. 26, 2018
Disaggregation of Revenue [Line Items]
Total revenue	$ 112,067	$ 112,178	$ 334,784	$ 329,567
Core Market
Disaggregation of Revenue [Line Items]
Total revenue	96,782	94,147	284,092	276,313
Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	15,285	18,031	50,692	53,254
Company-operated restaurant revenue
Disaggregation of Revenue [Line Items]
Total revenue	99,052	100,024	296,341	294,204
Company-operated restaurant revenue | Core Market
Disaggregation of Revenue [Line Items]
Total revenue	90,277	87,634	264,391	257,437
Company-operated restaurant revenue | Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	8,775	12,390	31,950	36,767
Franchise revenue
Disaggregation of Revenue [Line Items]
Total revenue	7,273	6,665	21,635	19,324
Franchise revenue | Core Market
Disaggregation of Revenue [Line Items]
Total revenue	3,696	3,712	11,369	10,697
Franchise revenue | Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	3,577	2,953	10,266	8,627
Franchise advertising fee revenue
Disaggregation of Revenue [Line Items]
Total revenue	5,742	5,489	16,808	16,039
Franchise advertising fee revenue | Core Market
Disaggregation of Revenue [Line Items]
Total revenue	2,809	2,801	8,332	8,179
Franchise advertising fee revenue | Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	$ 2,933	$ 2,688	$ 8,476	$ 7,860