Revenue from Contracts with Customers - Revenues Disaggregated by Revenue Source and Market (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 27, 2019	Mar. 28, 2018
Disaggregation of Revenue [Line Items]
Total revenue	$ 108,977	$ 105,756
Core Market
Disaggregation of Revenue [Line Items]
Total revenue	91,522	88,947
Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	17,455	16,809
Company-operated restaurant revenue
Disaggregation of Revenue [Line Items]
Total revenue	97,150	94,553
Company-operated restaurant revenue | Core Market
Disaggregation of Revenue [Line Items]
Total revenue	85,306	82,962
Company-operated restaurant revenue | Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	11,844	11,591
Franchise revenue
Disaggregation of Revenue [Line Items]
Total revenue	6,444	6,106
Franchise revenue | Core Market
Disaggregation of Revenue [Line Items]
Total revenue	3,499	3,376
Franchise revenue | Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	2,945	2,730
Franchise advertising fee revenue
Disaggregation of Revenue [Line Items]
Total revenue	5,383	5,097
Franchise advertising fee revenue | Core Market
Disaggregation of Revenue [Line Items]
Total revenue	2,717	2,609
Franchise advertising fee revenue | Non-Core Market
Disaggregation of Revenue [Line Items]
Total revenue	$ 2,666	$ 2,488