Revenues Estimated revenue recognition (Details) $ in Thousands	Mar. 28, 2018 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Deferred franchise revenue expected to be recognized	$ 21,928
2018 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Deferred franchise revenue expected to be recognized	1,646
2019 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Deferred franchise revenue expected to be recognized	2,105
2020 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Deferred franchise revenue expected to be recognized	1,981
2021 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Deferred franchise revenue expected to be recognized	1,769
2022 [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Deferred franchise revenue expected to be recognized	1,661
Thereafter [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Deferred franchise revenue expected to be recognized	11,270
Development agreements and unopened restaurants [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Deferred franchise revenue expected to be recognized	$ 1,496