Revenue from Contracts with Customers - Revenues Disaggregated by Revenue Source and Market (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2018	Sep. 27, 2017	Sep. 26, 2018	Sep. 27, 2017
Disaggregation of Revenue [Line Items]
Total revenue	$ 112,178	$ 101,155	$ 329,567	$ 306,499
Core Market
Disaggregation of Revenue [Line Items]
Total revenue	94,147		276,313
Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	18,031		53,254
Company-operated restaurant revenue
Disaggregation of Revenue [Line Items]
Total revenue	100,024	94,982	294,204	287,316
Company-operated restaurant revenue | Core Market
Disaggregation of Revenue [Line Items]
Total revenue	87,634		257,437
Company-operated restaurant revenue | Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	12,390		36,767
Franchise revenue
Disaggregation of Revenue [Line Items]
Total revenue	6,665	6,173	19,324	19,183
Franchise revenue | Core Market
Disaggregation of Revenue [Line Items]
Total revenue	3,712		10,697
Franchise revenue | Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	2,953		8,627
Franchise advertising fee revenue
Disaggregation of Revenue [Line Items]
Total revenue	5,489	$ 0	16,039	$ 0
Franchise advertising fee revenue | Core Market
Disaggregation of Revenue [Line Items]
Total revenue	2,801		8,179
Franchise advertising fee revenue | Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	$ 2,688		$ 7,860